There are 2 diff failsafes - one for loss of signal and other is for low voltage. Reading the manual, it looks like the only way to run with both off is to run the tx in ppm mode. It also appears to be an all or nothing type affair. What modea er you running currently?

This is page 17, if you don't have one, you can dnload it from the futaba website - look, it takes a little to find it, but they are all there.