Cracks are never fun. This one's in an awkward spot, too. It was happy to close up relatively easily but it's a tricky location for clamping.
Time for some out of the soundbox thinking (see what I did there?).
Cutting a block to match the curve of the guitar side in this area was an easy enough job. Now, I had my clamping caul and just needed a way to clamp. I drilled a hole through the caul. This allowed me to feed a bolt through the guitar's end-pin hole and through the hole in the caul. Snugging up the bolt pulled the caul in, closing up the crack.
Now, to the completely honest, I did add a long, sash-type clamp to give a little extra pressure to be completely sure about this. You can't put too much pressure on with that, though, as it'll start crushing things if you're not careful. The extra helping hand my bolt-clamp gave was just what the doctor ordered in this case.
Oh, incidentally, that caul is lined with cork and then packing tape. Its slick surface means the glue won't adhere to it. Otherwise, after this repair was done, I'd have a completely new, Caul-Glued-To-Guitar-Removal-Repair to contend with.