*can be sent
This is actually already possible, which I discovered by coincidence!
Just enter the whitelist you wish to use among the blacklists.
However, instead of entering a positive number, try entering a NEGATIVE SCORE (say, -3 for testing purposes), and being listed on that list will DECREASE the spam score of a message.
I suppose setting it to -10 would almost be the equivalent of white listing everything on that list (unless there is additional scoring from other lists).
So this is actually kind of implemented. Only thing it needs is a 'never block' option.