I used mirror lube for years when I first started casting bullets. It was a wax WITH moly in it. It worked just fine and I could NOT see any build up. Of course that was WAY before the internet so there was no chance for myths and internet rumors to develope!
I have and use a Lyman 450 sizer. When I want to do the traditional sizing/lube style, mostly for rifle bullets. I use NRA formula 50/50 beeswax/alox, Javalena or tamarak lube. The problem is; it doesn't ship well! As I'm finding out now that I've shipped some bullets to those that asked for them in my boolits in the mail thread.
Sounds like the cleanest way to lube the bullets is also the slowest....dipping them in hot lube. Some one said something about graphite, has anyone try'd spraying dry graphite on them? Seems like it would be clean and look good.
If by "hot lube" you mean melting a stick of bullet lube(melted) you would otherwise use in a lubrisizer, then I doubt enough would stick to the bullet to do it's job. There's a lot of theories about how lube works, but one that is true is the lube groove should be full of lube to protect from leading. Melted lube would slide off the bullet, leaving the lube groove only partially filled.
Lee used to make a cake cutter die that was used to cut bullets from a cake of lube that was melted and poured around bullets. That left hardened lube in the grooves. Since they came out with LLA, they quit making them. You can use a cartridge case with the head cut off to cut bullets from the cake.