The Tonfly system does look convincing - but:
I already have a RAWA helmet so i just need to add a cutaway system - and i spoke on the phone with Tonfly last week and i was told:
"The Tonfly cutaway system is not sold seperately"
So i keep on looking...
I also have a Nikon D200 and found this link useful:
http://www.gophotography.net/tips/release.html
You need to spend some money on a Nikon cable to connect to the 10 pin connection and then do a bit of soldering...but i could so most likely You can too
Anders B. Larsen