Selling memberships

Hi everybody,

I have commerce site set up for a non-profit customer of mine with the subscription products module installed. We're using the module to sell memberships in the organization and it all seems to be working, except that occasionally people buy more than one subscription under the same name, which means that my customer only gets the address info for one of the two subscriptions. Is there any way to limit an order to a single product so people must place a second order if they want a second subscription? We're only selling subscriptions and I don't think a single individual would want multiple memberships under the same name.

Thanks in advance.

-David