I have a no linked axle hub dyno, it just can 2WD or 50:50AWD car.

Does anyone know how to dyno a GT-R35?

The only R35 GTRs I've run have been i 4WD mode so I can't comment from personal experience. I found a thread on the GTR Life forum that mentions removing a front driveshaft - https://www.gtrlife.com/forums/topic/36038-running-the-r35-in-rwd/

Not sure if there's an easier way without reflashing the TCM or something of that nature.

This reminds me of there being a rumor how you could run a 997TT in RWD and that just doesn't seems to be possible without bunch of issues and is exactly that, a rumor. But I'd be interested to know if R35 can do it easily.

I've looked into it loads and spoke to a fair few people and they've all said pull the shaft is the simplest surefire way to run in RWD, you need to run the car up lightly until the 4WD system goes into fault before trying to load up the system.

I have never tried it so I really don't know for sure if it does any damage to the clutch packs or not but I don't see how it can as there will be no load to the front wheels