Why not try pyrocat-hd in 2:2:100? This is what Sandy recommends for alt processess that need extra density. (Azo Platinum and the like) I have never heard of soaking pyrocat-hd negs in spent developer. It was a part of the process for PMK pyro but has since been not recommended for PMK. PMK and Pyrocat-HD are not remotely the same formula. In the old PMK processess one was told to remove the film from the fixer and place directly into the spent developer. After 2-3 minutes remove and wash without KHCA. I don't know what would happen to the film if that is done to the Pyrocat-HD neg most likely nothing.

<<Kevin said, "I have this dim memory that normal processing of Delta3200 in Pyrocat yields an ei of 800.">>

This is my understanding also. I read in another forum that someone had good luck with D-76 at 68f for 14 minutes with HP5+ shot at EI 800. You might try this and see if it meets your requirements. YMMV.