Foliage Painting on Blueprint Actor?

I’m trying to paint foliage onto a Blueprint Actor I’ve made which contains several pieces of Static Mesh - basically I want to poaint a green roof onto the building blueprint, but the foliage paint won’t recognise the mesh as being paintable.

If I place the FBX for the roof into the scene manually, not in a blueprint, it is paintable. Anyone have a solution to this?