Yes. You can spend a force point to reroll if you have one. This would not be interrupted by the ability triggering (as in, your opponent wouldnt immediately gain control and be the one deciding whether or not to use the FP for a re-roll).
The ability doesn't trigger until after the save, you have a window of opportunity to reroll any save with a FP unless another mechanic prevents you.
Note: I'm way out of practice and if I was ever one of the "rules guys", i am not now. Someone else can should confirm this is right
