Snap to vertex with armature deformation

I have a character model and currently I’m working on corrective shape keys. To create some shapes I want to use snap to vertex tool. Problem is, that my character needs to have e.g. arms raised up, so that I can see how this corrective shape looks like. But when character is deformed by armature, snap to vertex tool doesn’t really work as I’ll want it to. Yes, it snaps selected vertices to each other, but it’s not taking armature deformation into account. It’s making offset from original, not armature deformed position, so finally snapped vertex is totally in different place than I want it to be. Any idea how to solve that problem?