I almost always perform the dine in BEFORE the drive-thru. Performing the drive-thru first is only a SUGGESTION and is not a requirement of the shop. I think they suggest it so that you have a better chance of STARTING both parts of the shop within the required timeframe.
Only once have I been recognized by a drive-thru employee who said, "Hey, weren't you just in here?" I replied, "Yeah. My spouse just called after I was in the car & wants me to bring home X while I'm here." It worked perfectly & I'm prepared to use it any and every time if necessary. In fact, I'm a little paranoid, so as I get to my car after the dine-in portion, I put my cell phone to my ear and pretend to be talking to someone.