For PIR, the best I know to recommend is talking to Prodrive. Unfortunately, their open test days are not backed up to an ICSCC weekend because the Cascade school always runs on that Friday. Still, you might look at their schedule and talk to them about when they allow OW cars (I know they do sometimes). Maybe you could do some testing and then move on to a different venue for an additional event?
Just FYI, the reason Cascade only offers a single session for OW is that the other 4 groups are always full enough to merit keeping them, whereas the OW interest recently has been very low. We wanted to give OW cars sometime before the race weekend started, but cramming one session in was all we could financially justify, and was all we could do with the time restraints.
If you can pull together a min. of around 15 cars, then I'm sure Tracy would consider assigning an entire group to be OW throughout the day. I offered this up a few years ago, though, and got zip for interest. Just saying. If you guys want track time, you've got to pull together to make it financially worth the clubs' time.