inverting space for a vapor barrier?

I have never had any trouble fitting a thin polypro liner, breadbag VBL and smartwool hiker sock into a boot sized for the smartwool.
If your having trouble with a THIN liner sock maybe you sized the boot too small?

How the heck do you place a polypro sock, a vapor barrier sock and an insulating sock in the same boot which you had fitted for just a regular insulated sock?

Would not even try. VBL being suitable only for temps below 30F and wanting to handle walking in snow down to -10F (maybe colder), I'll buy boots to use only in winter and size them up to accommodate the socks needed while walking.

If the boot is too tight for all that you could just try a thin liner and a neoprene sock. Wool is great for taking up sweat but if there is a vapor barrier inside the wool, then a neoprene sock insulates well for it's thickness. Just don't wear this combo to bed; put on fresh dry socks when sleeping. You also might want to consider antiperspirant on your feet if you are in conditions that require long term use of vapor barrier socks.