provided by Star2Billing S.L.

Is there any way to do this?

I know security wise it's not as good, but my plan is going for calling cards that are in the $5.00 range. I want to eventually have a customer support call center where users call in with their PINs (AKA their Alias), and then the call center staff can look up their balance, usage, minutes, etc through the client interface.

Do you have any suggestions?

There's no setting for this, but it's a trivial modification on line 87 of A2B_entity_card_multi.php to do what you want.
As for the security implications, if you're running pure calling-card service with no SIP clients then I'm not aware of any real problems of making the cardalias = username.