I delved a bit in the source code of the tilemap, and I don't think it's reasonable to have a plugin to do that. The collision engine is deeply rooted in the C3 core and most of its code is external to plugins.
I think it would be better to have Scirra officially support this. Maybe by adding a new tile state to its mask (i.e. collision disabled flag) ? A tile state already flips the collision polygon accordingly, maybe a new state to entirely remove the polygon for said tile is easily feasable ?