Here's the situation. ENG environment, in large crowds interviewing people at random. There is no second take, and there is no room to run a breakaway cable from the camera to the interviewer.

Currently using a Sennheiser MD-46 with a plug-on transmitter to a receiver on the camera. Camera man can monitor the handheld and the shotgun mic on the camera. Shotgun acts as backup audio if handheld placement isn't ideal. Sometimes the interviewers aren't great with the handheld mic. Their reasoning is that they can't hear the audio, "if only they could hear it!"

What are my options? Mounting a second receiver with an earpiece on the interviewer seems like the easiest way. Bulky option is wire the handheld mic to a small recorder/mixer then to a beltpack transmitter to the camera. What is everyone else doing?

Take a look at:
Sony ECM-AW4
Wi Digital JM-WAL35

Sennheiser IEMs for me - and bags of audio level.

A second receiver with a IFB news earpiece (if the interviewer is also on-camera talent), is probably the best option.. Problem is... the EK100 portable receiver does not have an actual HP output (but the line out 'may' work, depending on how loud is needs to be), so a separate HP amp may be needed. OTOH, the 500 and 2000 series portable receivers do have HP outputs.. and naturally cost more.

Agreeing with what's written above... but...

Moving a hand-mic is a skill that can be learned, and learned best with time dedicated to learning. Thousands of interviewers pull this trick off every day without wireless monitoring.

I'd suggest that you share some of the resulting recordings with the interviewer(s), then have them interview you with a hand mic while wearing cans with good isolation. A little practice in this way might do everything you and they wish.

This also can keep you from increasing the complexity of setup and operation. If it were me running camera and monitoring two sources I'd think that was enough without adding another wireless link.

I would say either the Wi Digital JM-WAL35, JM-WAL35MP or JM-WI-ALP55 Pro would work for this purpose (as well as many other uses).

Some vendors are saying some of these various configurations are discontinued, other vendors still have them in stock.

Essentially each configuration goes up a little in price and capability.
The basic set would do exactly what you need as long as there is a free line or headphone output from the camera's receiver or the camera itself.

The MP set adds a USB transmitter for transmitting audio from a computer or tablet, say for playing back edited instructions or music for an on-camera talent to follow or act/dance to.

The Pro system has USB capability built-in, as well as line or headphone input and output.

There is also a Wi system that has head-worn mic inputs and mics, but you don't need that one.

I have the basic kit and just added the USB transmitter. They have worked fine for me on several projects. Mostly for monitoring the wireless boom without being attached to the camera. The same type of situation you want but for a handheld mic. I've had no complaints.

Sometimes the interviewers aren't great with the handheld mic. Their reasoning is that they can't hear the audio, "if only they could hear it!"

Meh. Yet another version of "blame the sound guy" ?

My experience is, some talent understands a hand held mic. They listen to what you tell them about how to use one, where to point it, how close to get it to the interviewee's mouth. And then they do it. And damned if it doesn't work. Amazing. Everyone happy.

And some talent, just can't figure it out. They look at you with a blank stare, refuse to believe anyone else can tell them anything at all about how to do their job, won't point the mic where it needs to be pointed, won't place it close enough to the interviewee's mouth, or their own, and they pull the mic away before they quit speaking (a personal favorite of mine). They just won't be taught. And damned if it doesn't fail. And damned if it isn't the fault of the equipment, the sound guy, "if only they could hear it", the sun's in their eyes, gravity is too high here, the paint is the wrong color, whatever. The fault is anything but them.

I'm just sayin' that some days are better than others.

While the usual receivers come up second hand from time to time, the IEM receivers are rarer, and go for decent money. The comments about not needing the feed to learn did make me smile because we rather repeat the mantra that to record decent audio, the cameraman MUST listen to the audio - yet deny the option to the reporter. Mic technique is so much easier to learn when you can hear what you do.

NEVER underestimate the ability of "talent" to mess up your day... :-)

The IEM receiver in the same band can tune in the mic transmitter. Just turn off the pilot on the IEM and set it to the same freq., which you will prob have to tune manually as the presets aren't the same on mics and IEMs.

It's a talent problem...... Fix or replace.

An Omni mic held high and between the talent and interviewee might be a good starting point.

While the Sennheiser MD46 is a highly regarded mic, it is cardioid and not quite as 'forgiving' as the Omni directional MD42... but it's still not a substitute for experience.