CD has it dead on. I have done that for 2 parties in the last few weeks, and numerous times in the past. The people wanted the pulled pork for an event in which I was unavailable to attend.
I cooked, rested, and pulled as normal, put into half pans (one shoulder per pan) then off to be cooled. For reheating, I instructed them to add about 1/2-3/4 inches of aple juice to the bottom of the pan, cover tightly and then place in a 275* oven for 45 mins and occasionally flip the meat around with tongs. Once it was hot enough, turn the oven to 190*ish and it can sit there all afternoon. When doing the initial heating you want to make sure you don't boil off the apple juice, so you may need to add more, once your just holding it, the juice temp should be low enough to not burn off.
Your guests will never know that you didn't pull it off the smoker just prior to their arrival.
***As a side note & disclaimer, I never serve customers this way on events which I'm catering unless I have informed them prior. They wouldn't know any difference, but to me it's still the principle.***
Homemade trailer Roaster a.k.a "Hog-A-Nator"; UDS; Dual Chamber Charcoal; ECO Gasser