Here's an awesome exercise borrowed from FRC (Functional Range Conditioning) that we do with pretty much every client. The "hip 90/90" or "shin box" position allows you to activate both glutes at the same time while you actively work through the range on one side, and statically hold a contraction on the other.
Turn the sound up to get cuing for how to perform this movement properly.
Ideally you would be able to perform the exercise without needing your hands to help. Reese has some hip and spine restrictions that are keeping him from performing this perfectly, but you have to start somewhere! Hopefully we can post a follow up video of him crushing this drill in about a month from now.