For me the key was finding a suitable substitute.
Here’s a recipe with a 100% yum-rating from Virginia smokers.
I’m waiting on my AIO Pro to come back (loaned it and this juice to my ex-wife who has now quit) so I can carry it with me for smokers to try.
To your friends’ good health! 
I might order up the remaining ingredients needed to make this one.
I’ve been on the fast track trying to get my wife to switch. Her smokes of choice are Marlboro menthol.
I don’t have any tobacco flavorings so she has had to settle for mostly fruity menthol flavors. I think this may be a good starting point.
Perfect that she’s a Marlboro girl ie someone who likes taste in their tobacco rather than burnt leaf-matter like many of the budget cigarettes. I really hope she enjoys this recipe!! (recipe name and comments edited to account for menthol smokers )
Please let us know how your wife goes and any mods you make to the recipe
Anything with a little mint or menthol stuff help. The first vape I had that sold me on it was a berry mix with a mint sting.