Buy FlavorArt coffee espresso concentrate. It tastes exactly like espresso, but be warned, it is the single most potent flavour known to man. I mixed it at 1% and it was SUPER strong. I then added a few drops of that mix to a full tank of a different juice and it totally dominated that juice also. I think the best way to use it might be to mix it with PG at 1% and then use that as a concentrate at, fuck knows, I haven't found out yet, but probably 2% would be a good starting point. A 10ml bottle should last you forever.