We once managed to get DD on Indy due to the fact that she was wearing a pair of those flips that have the elevated foam sole. They must have measured her 4 times and again as we were entering the vehicle, but they still let her on (she was about 5 or 6). I thought they wouldn't and regretted that we didn't have her in regular shoes because (a) it was a hassle, (b) it made her think there was something extra scary about the ride, even though she loved scary and (c) she didn't enjoy the experience because of it. Well, that and the fact that she was terrified of the giant snake! I had wondered why Indy was a different height requirement than ToT, Splash, Space, etc. Turns out there are some good reasons.
On the other hand, I have a different issue with my grandson. He is almost 6 and is very small for his age. He's dying to go on RSR but he isn't quite tall enough yet! If I could get him on with a little higher tennis shoe, I would be tempted. He's old enough and ready for the ride but he's too small. I don't know if that poses a safety risk or not, but he's so disappointed every year that he still can't ride it.