Ok did some quick googling (on kayaks) and this one site shows a plastic rod that you melt into the crack to fuse it back together.
http://www.oceankayak.com/product_support/repair.html
So that's an option but sounds a little labour intensive and maybe a wild goose chase to find the parts (heat gun and then the plastic rod itself - although call around, I bet some kayak/canoe store, maybe even Mountain Equipment Co-Op) has something. So maybe first try the silicone idea .. just use a generous amount of a glop over the hole .. and failing that, maybe see if PVC or ABS cement might work.
Good luck!!