I did a lot of plastic repairs last summer on various things and learned that glues, epoxies etc usually are not easily attached to plastic for repairs. I did have great success in welding plastic by using a plastic welder bought at Harbor Freight, basically a soldering iron with a flat tip. You would need similar plastic to use as a filler -they sell rods made of ABS, and few others (maybe spare washer caps around) or just determine what kind of plastic it is, I think its probably some type of polyethelyne -if it floats most likely it is. (nowadays plastics are marked -there are guys on here that can probably tell you what kind of plastic it is).
Ive used things such as milk containers,totes etc and even just shaved excess material from the item to use as filler.
a few sources:
http://www.urethanesupply.com/identify.php
http://nerfhaven.com/forums/index.php?showtopic=18527
http://grumpiornot.hubpages.com/hub/How-plastic-is-really-recycled
Again I humble myself to the more knowledgeable folks here.