Its probably not a good idea to merge this with the tk2dSprite class - the sprite class can work with any number of vertices (used in diced meshes), whereas the clipped sprite is limited to 4 vertices. Also, there are more classes like this coming in a future release (9-slice with tiled background), so it isn't really practical to do it like this.
You can't generate sprite collections at runtime, I'm afraid. I can see how it would be useful, and this actually has been in our TODO for a while now, but its very low priority and high priority things keep cropping up all the time.
unikron