I have a hard time believing anything could come out of the back two bomb bays in the configuration. Everything I've heard is that the turbulence between the nacelles gets really bad. I read once that the B-1 was limited to just sixteen Mk82 (500#) JDAMs and when I actually found a guy who claimed to be a B-1Nav named Calvin, he confirmed. I asked him about that; he said that to drop that size bomb they had to use the same rack as the CBU-87s (10x per bay) but that ordnance had separation issues - the front bay could carry the full ten, but the next one only four, and the back bay only two, for the total that I'd read of sixteen. I assume something about the aerodynamics or weight of TMDs allowed for the full number to be carried. But point being, that's rough air and I doubt lining the area around the bomb bays with draggy pylons and 3000lb missiles is going to smooth it out.
Academic I think, because no one is investing any time or money getting the externals operational (outside the SNIPER pod) on the small number of tired aircraft that are combat coded. B-1 is I think the first platform due to be replaced by B-21 now.