They sell aluminum wheel hexs to replace the plastic ones. This works pretty good. But since the hexs in your wheels are already stripped you will probably be replaceing them. I would recomend going to a 17mm hex adaptor. Much stronger than the 14mm.
These are the ones I like:
http://cgi.ebay.com/OFNA-81175-HUB-A...QQcmdZViewItem
These are also good from what I have heard.
http://www.rc-monster.com/proddetail...er_2330&cat=42
They will both require 17mm hexes in the wheels. There are lots of options out there for that.