Do glycerin and non glycerin soap mix?

I have a hard shaving soap that I had grated to press into the shape of my scuttle. The problem is that because the soap is hard it had trouble taking its new shape. I tried to melt a sample of this soap in the microwave to see if it was glycerin based. It just shriveled. With a different soap I tried mixing it with some moisturizer as a binding agent. That just turned it into a good hand washing soap.
So I was wondering can glycerin be used as a binding agent to help hard shaving soap form into a mould?
Any suggestions would be greatly appreciated.

If you want to convert it to glycerin soap, you need to melt it in high purity alcohol. Vodka works pretty well.