This is probably a really dumb question but.....

I want to record sound externally with a zoom HD4 using my NGT3 mic, but I also want to attach a Rode videomic to the camera so I can synch the audio later.

The camera will be hand held and I will be moving around quite a bit and I'm filming solo so no one to hold the Zoom for me.

Do I have to attach both mics to the camera? If so how?

Are there other alternatives?

Get a flash bracket like this:
Amazon.com: Adorama Heavy Duty L-bracket with 2 Standard Flash Shoe Mounts: Camera & Photo

And one of these for the Zoom:
Amazon.com: Marshall V-LCD-MT Monitor Adapter 1/4" Mount Adapter To Video Camcorder Hot Shoe For LCD Monitors: Electronics

The flash bracket gives you two extra shoe mounts and a handle for handheld shots. The shoe adapter makes it so you can tilt the Zoom and monitor levels.

Thanks Andy.

Have just ordered the parts.

this looks interesting for connecting multiple devices to the camera:

Amazon.com: ALZO Shock Multi-Mount for Microphones & Audio Recorders incl. Zoom H4n - & DSLR Video Recording: Camera & Photo

Thanks for sharing the link this is really helpful.