Another work-around would be to use case filler between the powder and the bullet. The filler gets pushed up against the base of the bullet and serves as a gas check. Most fillers when compressed that way also serve to scrub any existing leading out of the barrel. There's at least one commercial product for this, really tiny little plastic balls so fine they flow like a liquid. If you're cheap like me, uncooked cream of wheat cereal works well.
Couple of downsides or potential downsides. One is to carefully work up any loads for which you use fillers. The mass of the filler is getting pushed out of the barrel in addition to the bullet, so pressures will be a little higher than with bullet alone. Also, even though it's compressible, the filler will reduce the volume inside the chamber into which the gases can expand, which will raise pressures. And finally, powder burn rates are affected in a non-linear fashion by chamber pressure, with high pressures leading to much faster burn rates and thus higher pressures. Carefully work up any loads with filler.
Another downside is that adding the filler material adds another step to the reloading process, which makes it go slower.
That said, I've had a lot of success using cream of wheat filler in pistol using W231 powder (9mm, 357, 40, and 45) as well as with cast bullets in rifles with BL-C(2) and several IMR powders. I use cream of wheat filler in all my cast rifle bullet loads. I'm still tinkering and adjusting, but I can push lead bullets faster than will allow them to spin stabilize, like 2300 fps, with no leading and no gas check other than the filler material. I slow the cast bullets down so that they'll grip the rifling and will spin stabilize, but that's the only concern, leading is not a problem at all. I love plinking with my 30 Carbine and being able to use my own cast bullets in it means I can plink for less than 10 cents each (just powder and primer) all I want, so long as I don't mind spending a lot of hobby time reloading. Ditto for my 8mm Mauser and 7.62x39 rifles. Even for 357 magnum, I like being able to make some pretty hot cast bullet loads and not worry about leading.
So, you could potentially try shooting lead bullets with some filler in a polygonally-rifled barrel. For pistol I usually only make limited amounts of these, because it's extra hassle to have to add the filler. At the end of a range session shooting lead bullets, I'll run 15 or 20 of the cream of wheat rounds through the gun to clean out the barrel.