I don't know how well straight stevia would dissolve into a VG or PG solution. I guess you could try it, but if you see particulate matter remaining, I might abandon that choice. . You'll also have to figure out what percentage you need to place in solution to use for your sweetening events.
I'm not saying it's impossible or anything (I simply don't know enough about stevia to say, I use sucralose) but doing this would probably require some trial and experimentation, if it can be done successfully at all. Which I don't see an immediate reason why you couldn't, it would probably be a matter of researching it more, and seeing what solution percentage and dissolving process works best for stevia.
Good luck, I hope it works out well for you.
Anna