I would like to brainstorm a few ways of handling how to detect a collision between a sprite and a user generated shape of some sort.

For example. There are 3 objects on the screen. The user takes their finger and draws an abnormal shape around 2 of the objects. I need to detect those 2 objects.

alt text http://desmond.yfrog.com/Himg339/scaled.php?tn=0&server=339&filename=f2i.png&xsize=640&ysize=640

Anyone have any good ideas on how to approach this efficiently using Cocos2D?