I think the order desk can route orders to the MM of the customer's preference. The software I learned to trade on allowed that. We could preference anybody we wanted and print their shares at whatever price they were showing.

I know from experience with these folks that brokers can route sell orders to whatever retail MM they have a contract with. I would think buy orders would be no different.

Next time somebody wants to take out a specific MM, ask the broker if he can route it directly to that MM. Then demand they waive the call in fee!!!! LOL