I've been using a software solution for quite a while. USB over Network from Fabulatech.
You need to install a server on a physical machine to plug the USB dongle (an Aladding Hasp Key in my case), then just install clients wherever you need them, and connect.
Support is quite fast, and I could try it for a few days to check it fitted ou enviroment, as I wasn't really sure (how could I!) and the software I planned to virtualized was critical and offered no license management alternative.
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