As far as I know the only Valve Bodies that do not apply the band in low gear are aftermarket race versions that deleted this function.

If I were running a "Shift Kit Valve body" I would probably start in 2nd as Pbody suggested. The reason right or wrong is your trans is still going to start off in 1st no matter what you do. So at least it will cause the sprag to seat the rollers where if you are in low, you are applying the band and not seating the sprag. A manual rear band apply valve body would be a better route. A few hundred for a front drum that will not blow, even better. I would say a low power combo may not be threatened by a sprag failure, BUT.... I have seen a 4WD pickup out playing in the mud blow a tranny up. So it can happen. A blanket can be used but you will still bend up the floor board.

Leon