I just got signed off on Indiana last Sunday and I completely forgot to ask. It wasn't mentioned in my training, so I want to say no that option is not available to you. We can vent the hydralics on a vehicle, but I've never heard of them doing that and allowing Guests to ride that vehicle.
DanC would know the answer, since he's been on Indy for a while (I think)... but he got himself banned from MiceChat over some stupid comment that he shouldn't have made in another thread.
Anyways, next time I go in for a shift (Sunday) I'll be sure to ask and let you know.