The FT TC4 Battery Strap #31126 (http://www.teamassociated.com/parts/details/31126/
) will work with lipo batteries.
I own a FT TC4 and have used several different lipo batteries with that battery strap. An additional option would be to use the FT TC4 battery strap above and instead of using body clips to hold it on, use FT Battery strap thumb screws #1787.
Personally I feel the legs on the FT TC4 battery strap are a bit short. What I have done in the past is use longer hex head screws to hold the battery down. You could use a longer 4/40 threaded rod and the thumb screws.
Another thing about the FT TC4 battery strap is that the lipo battery isn't a secure side to side as I would like. My solution was to use velcro on the top of the battery/bottom of the strap to keep it more secure. You could also use double-sided tap if you only use one battery in your car (which is what I did when running VTA).
It may be hard to find the FT TC4 battery strap at this point. I believe that the TC5 battery strap parts would also work on a FT TC4 but may require some minor modifications.
If you do use strapping tape to hold the battery down, be advised that it will pull off any decals on the batteries (unless you use something to protect them - such as plastic shrink wrap for battery packs).