Sodium Bicarbonate blasting is a good candidate, other than getting power and equipment and a ton of bicarb to the site is not trivial.
It occurs to me that if the acrylic is slathered on thick enough, liquid nitrogen might work. You've seen what it does to lettuce? Just pour it on & the paint should just shatter. I would imagine that the "tendrils" connecting it to the rock would shrink & lose grip. Easy cleanup. Transporting liquid nitrogen in a Dewar on a trail, though, is a different problem - certainly wouldn't want it in my pack if I slipped & fell.
