Get yourself down to a comfy surface and place a weight behind one knee as you lie down on your stomach. Fold your arms in front of you, placing your hands in front of your chin so you can rest on them so your neck isn't unhappy.
Bend one knee and flex the foot. Think about the foot being able to balance a tray on top of it. Tensing stomach muscles, lift that bent leg toward the ceiling. You want the pelvis to tuck a bit so there's no undue pressure on the lower back.
The leg won't go far, but you'll feel your glute and hamstring fire up fast. Lift and lower as many times as you can in a minute, and then switch sides.
Even if you don't have a weight, you will still feel the workout lifting that derriere.