I would assume since uberlather contains glycerin that it would be ok to add it to creams, but I'm at a loss as to how you obtain it? Is this something you can just find at a Walmart or something like that?
WalMart will do it for ya, just look in the skin care/first aid section rather than over with all the other hand/body lotions. Mine was manufactured by Humco, and cost about $4 for a big container. While you're there, it's probably only a foot or two away from that cheap, generic Witch Hazel - so pick up some of that too!
I'm actually up in Canada so I'm limited to Walmart or Drug Stores. I was able to find some glycerin though. Now, how much would I put in my mug for each shave? I would assume very little.
Just a couple of drops is enough.