Well, how about putting a Filtertron in there, they are probably the twangiest pickups around - TV Jones sells them in HB-size (expensive, though).
I have some old GFS Brookly pickups - HB-sized single-coils - that sound rather twangy; I think the Brooklyns aren't available any longer, but I've heard the GFS Dream 90 is actually a Strat-type singlecoil in HB-shape, so it might get you closer to twang.
Or you could ask someone like Pete Biltoft from
www.vintagevibeguitars.com to wind you a HB-sized singlecoil that will twang - he actually has HB-sized P90s, but with Alnico slug pole pieces instead of bar magnes and pole-screws, and those, maybe a bit underwound, should probably get you as close to a twangy sound as possible with a HB-routed guitar.