Spray animation question

Hey guys/girls at the animation forum,

I’m busy with a blender game with cutscenes. One of the levels has a ghetto style and when I think of a ghetto, I think of graffiti. With this in mind, one of the characters has to “tag” a wall during one of the animations, but what’s the best way to animate the paint? For the paint cmoing out of the spray can, I was thinking of using shape keys, but how do I animate the paint at the wall (so the tag has to be drawn in real-time)? I can’t use much blender notes, since it’s BGE.