I used AT rafting back in 2011. It's a small company so my guess is they will be flexible. The owner is a bit of a curmudgeon, but you would be too if you employed 19 year olds all summer long.
AT runs Seidels and Twin Falls (or at least they did), which is an added bonus. Cost was pretty reasonable too (some of these places want to charge $700 or more).
The clincher for me is that he agreed to let me run Browns twice in an oar frame before the end of the two weeks. I have no interest in actually guiding people and knew my long term goal was multi-days in an oar frame. I did have to remind him, but he held true on this. Having said that, I think that Noah's Ark trains on oar frames if that matters. I suspect they won't be as flexible though.