Editor vertex paint on sub objects only - how?

i have static meshes with multiple subobjects separated by material id, in this case it’s wooden chair with velvet padding. Then i have blending material(s) with vertex color as a mask to assign wet surfaces.

I want to use editor’s vertex paint tool to paint wet areas but in places where chair and padding are close together i always paint on both of them even when i want to paint only on the chair and not the padding.
Meshes and their vertices are not connected, just exported as one static mesh.

Is there a way to ignore sub objects of the static mesh i am painting on?