How to Handle Abilities That Grant Rerolls

There are lots of abilities in the Pathfinder rules that allow players to make rerolls. In particular, I'm talking about abilities that force opponents to roll twice and take the lower result. Is there a way to implement this when applying spell or other effects to saving throws? I think I can handle it manually for attack rolls (although an automated way to handle that would be great), but trying to manage that for a large group of enemies targeted by an area effect would be cumbersome.

If this isn't already implemented, I'll be adding it to the feature request for d20Pro Unlimited.

Thanks!