I can do this for you, on one condition, that I can multitask and create one for WalletBit at the same time.
I have just finished creating a PrestaShop Payment Module, and if you'll like I can build it with Bit-Pay's Shopping Cart Interface as well.
You can see the PrestaShop Payment Module in action at
http://loja.pmakordeoneditora.pt/pt/Kind regards
Kris