LOL!
I think my advice (in general, not necessarily for McD's), would be to order only one small item and stand there waiting for them to make suggestions while staring at their badge, running your eyes up and down them, leaning over to look at the fries bin or the cook line or whatever, etc! :-)
I know that another discussion asked if people ever pretend to be a bad mystery shopper in order to get better service. I have to admit that it is tempting at times! Hmmm... maybe only at places that I would never actually shop.