I'll ask why do I have to pull up and the person will usually say something like "there's a timer so as long as I'm parked or stopped on the timer it looks like they are running slow." Well, technically they are. Do I have the right to say, "no, I'd rather wait here to get my coffee or food order."
Of course you can - you can also berate the poor person working at the window if you want to - not that I would suggest you would do so.
Couple of personal thoughts on this - if you really do not want to pull over and I can see your point seems a bit dumb for you if you do have something simple - just say thank you, but I'd rather wait here. I'd always be polite and kind, I mean these poor people probably get jerks all the time cursing at them and so forth - just respond nicely and politely.
The other option - go ahead and park - read through your phone while your waiting and then when you get home - typically there is a receipt with an internet address to take a survey - convey your dissatisfaction with the fact that this fast food restaurant utilizes the pull up to skew the stats on their speed; maybe corporate overall will then change the policy if enough people mention this.