There is no shame in using a little DME either. Don't get caught up in AG as dogma. It is a great approach, but use the tools available to you... I have frequently used some DME to reach target OGs on batches made from second (or third) runnings. It is pretty cool to add two pounds of DME and get a decent additional session ale out of your brew session for the price of an ounce of hops, a couple of extra specialty grains, and another hour on the burner.
I have also used DME to provide constant feedings to a barley wine that approached 20%ABV. I guess it's not "all grain" anymore... But it is mostly grain... And doesn't require crazy brewing gymnastics just to apply some superficial tag to what is bound to be a very special beer regardless.
What I would do in your case is come up with a recipe for a slightly weaker than normal beer. Take a first running to feed the barley wine, just a couple of gallons (once reduced by boiling) with a high OG.... And then take a generous second running to produce a respectable beer. And then, maybe take some third runnings, combined with some DME for a third batch. Doing it this way, you can give away a LOT of beer, or build up your reserves, and feed a barleywine project at the same time with minimal loss of grain efficiency.
