Push ups on a bolster or walk outs are wonderful for trunk strengthening, body awareness, and a great addition to any obstacle course. You may also have client lay supine on top and try to align their body with the bolster. They may even be able to balance on it by lifting their feet off the ground. Push ups can be done with ankles or hands up on the bolster.
Bolsters make a great addition to any indoor playground.
Let your client walk out on their own or do it with them. If they need it, spot them at the hips as they move outward.
BTW If you do not have a bolster, try using a trapezoid or exercise ball instead.