Actually, on the treadmill, if you set the incline high and lean slightly back, (rest hands LIGHTLY on TOP of console only to support, NOT to "hold onto")....so you're not climbing forward, you're almost "pulling" yourself up, and force a glute contraction, you'll "feel" your glutes more.
Another option is doing the stairs (either really do stairs, or use a stairmill). Slow and deliberate, and don't support your weight with your arms.
Try a spin class. A good spin instructor worth their salt will make it hard for you to sit the next day...(if that's what you're looking for).
But as everyone has already said,....if you're trying to reshape your glutes and nice rear view, you can't under-estimate the importance of a solid weight
training routine.
Curtsy squats are devine for the behind (but only if you're advanced, because if you perform them wrong it's a good way to injure your knees and low back).
As Lady C said,....squats and lunges,...the Makers and the Breakers of any
Leg workout. Ooh, ooh, another goodie to add would be Step-Ups (with deliberate emphasis).