It may be too late to modify the sculpts, but the hole at the handle end of the weapon's shaft had a leather or sisal strap that went through it and then around the warriors' wrist. This was a further precaution against dropping the weapon during the battle.
If you are making separate weapons, please consider the tepoztopilli, or slashing spear. Here are some high level warriors armed with tepoztopilli from the Codex Mendoza:

Looking forward to your output in 2014. Also, any idea if you will be getting a distributor for North America? Happy Holidays.