[Unclenick]

There may be some validity to the idea from the standpoint of developing radial hydraulic pressure to help expand the tip and help prevent hollow point clogging by hair or hide on its way in. A blob of silicone dielectric grease in the cavity sealed in with silicone RTV should do about the same thing, and it requires no heat so it's safe to do on ammo that's already loaded.

You could try shooting that creation into a ballistic test medium to see which whether the bullets thus treated or those left untreated really open up first or most reliably. I'd have them pass through a layer of old handbag leather placed over the front of the medium to mimic clogging performance. Don't be surprised, though, if the untreated bullet does as well or better than the treated one. Unlike self-defense ammo, bullet makers get to test their hunting products on game, so they usually have a pretty good handle on how to optimize them without your help.

Another drawback to mercury, other than those already mentioned, is that it adds to bullet weight. That will raise pressure if the load was developed without that added weight. Silicone grease shouldn't add enough weight to matter, and it is used to lubricate food handling equipment, so it's environmentally pretty safe.