MyBB Community Forums

Hello mybb community, I was wondering if anyone could help me modify the shop plugin i have on my forum. I run a gaming community and on our site we use the shops plug in to sell in game items using paypal, problem is I need to know the player's steamid so I can actually give them the product. The problem is, the only notifications we get is an email from paypal saying buyers name, email, and product but sadly I don't know every forum member's real name so I can't run around asking who bought this. I was wondering if somebody could modify the plug in and add a steamid field that is mandatory for purchasing items. It could be on paypal or on the plugin itself as long as I get contacted with the product purchased and the steamid.

Here is the plugin link.
http://mods.mybb.com/view/mybbshops-free-lite-version