There's a step between being a Starbucks customer and being a Starbucks shop. See for example http://www.starbucks.com/business/office-coffee
I don't know how costs would improve/get worse, but I imagine it would at least be operationally easier if you could brew on the road rather than constantly having to go back to the shop, and dealing with drinks getting cold.
Potentially I can imagine them selling you branded equipment (cups, tissues etc.), coffee (just big bags) and the extras you might need (e.g. syrups), then as long as you made it well, so as not to give them a bad name, they could just leave you to it.