I don't have the current eXchange model, so I can't use daylight balanced florescent bulbs. Is my best option to search out for a huge sheet of CTB and tape it to the outside of diffusion? Would it be too hot on the inside if I used a small piece of CTB and tapped it inside at a narrower part of the "cone"?

No advice on an internal position, but if you try it write back and let us know how it worked out!

I've used CTB with my Rifa55s a few times, C47 to the outside of the diffuser, it's very worth while getting some 3/4 and 1/2 CTB as well. The full cuts so much output, and I've been able to do quite well with 1/2 and 3/4.

Getting material big enough for an 88 means finding a supplier that will cut it off a roll for you. I'd guess that in a city like Boston that won't be a problem, maybe your favorite lighting and grip supplier does this.

I regularly clip 1/2 or 3/4 CTB to the inside of the diffusion on my R-55 (gels just a bit longer than the diffusion dimensions to provide clipping surface)

I've used sheets gel both inside and outside.
Honestly, I would stick to the outside. As you know,
the sheets are actually smaller than the Rifa88, so I used
clear cellophane tape to make the gel large enough to cover the box.
Some don't bother.

My main issue with using 202 or 201 is the low transmission level.
I think L-201 averages about 35% transmission and 202 = 50%.
So that 1K becomes a 350 watt or using 202 a 500w.