The DBPro board would probably have been more help to you than here (it's mostly artists, not coders) but I'll try to give you some pointers.
Firstly, you may need to try to work out the 'normal' of the polygon you've hit - I think that there's a plugin that returns the normal of the collided polygon (not sure which one, sorry). That'll give you the angle that you hit.
After that. you'll probably have to have your plane with the sprite on it, actually be subdivided (like a mesh instead of just four vertices) and then do collision for each vertex and do some vertex manipulation. Once you get to corners, you may have to colour the vertex transparent if the distance is too great compared to the other distances.
Hard work, and some rather difficult maths - the DBPro board could help you more.