use bbg duck for Peking duck?

To crisp up the duck skin, rubbing the bird all around with clear transparent lard of pork fat, called manteca de cerdo. This is used here in Spain to crisp up a suckling piglet which the country is renowned for. All butchers can supply this, and it looks like white cream

and is tasteless. It truly works for crispness on roasted chicken too.

You can't really make "Peking duck" from a barbecue/roast duck.  Peking duck is a process involving complex defatting, not just a presentation.  

If you're reheating the duck whole, the lard idea is not at all bad -- providing you have good lard available locally.

That said, you certainly can remove and crisp the skin from a take-out, Chinese-deli barbecue duck, and serve it with pancakes, scallions and hoi sin or other "duck sauce."  Not quite the same, but not at all bad. 

FWIW, barbecue duck with the Peking duck fixings is a common eat in/take-out item on many a menu.  Just don't call it Peking duck.

In addition to being prepared differently, Peking duck is often served "three ways."  The first involves removing the skin and the best meat, and plating it.  Pancakes, sauce and vegetables (scallions, julienne of daikon, jicama, etc.) are served along side the duck.  The second is a room-temp salad made with sprouts along with most of what remains of the duck meat; it's a very light presentation and something of a palate cleanser.  Finally, the third way is duck soup.  The soup is made by boiling the carcass in seasoned water (and sometimes a little light stock as well), then the sparse remaining meat, a few greens such as watercress or chives, and squares of medium tofu are added.  Because it's boiled, the soup is quite turbid.

If you're serving a "to go" duck whole, you can't do three ways.  You could remove the carcass along with whatever sticks to it and make a quick soup.  However, "to go" duck is usually chopped before going into the container.  If you want whole, make sure you say so in advance.  Similarly, if you don't want the head included, tell them at the store.

BDL