[Plugin: Advanced Events Registration] Add a t-shirt purchase at time of registration?

I just installed and set up this plugin and am really impressed. I currently have one event registration set up for a $5 fee. Works great, but I was hoping to allow people to order a t-shirt for the event (and select a size) for an additional $5 (i.e. people who select a t-shirt when completing the registration form would be charged $10 instead of just $5.). Is this possible with this plugin or does it have to be a separate transaction.