I missed this whole thread previously. I'd be interested if you could make it happen. Unfortunately, it will mean workload on someone. Be it a mod, or Jeff (webmaster). I think the logical way forward would be to place a fixed order, pay for it up front, and then sell them as a membership package (payment only by paypal). I don't know, but I get the feeling Jeffs a busy man, and might not have the time on his hands to make it all happen. I know I don't..
Rzide? Any chance you could contact Jeff and make up 3 x templates to narrow down?
The other option is that people make their payment up front by a certain cut off date. At that point shirts are produced, and someone takes on the task of handling postage - again, tedious and hard to factor in varying postage costs.