I tried this last night:
I had some mild tobacco liquid I wasn't too fond of. The liquid was a very pale amber color.
I put about 3ml into a small plastic mixing bottle.
I put regular ground coffee beans into the bottle - filled the juice with enough grounds to just let me be able to shake the mixture.
I wrapped it in a paper towel and sat it on my candle warmer for about an hour, keeping a good eye on it to make sure it didn't get too hot, just warm, and kept shaking it periodically.
I started to notice the liquid getting darker in color.
In a separate bottle I put about 1.5ml VG+distilled water (premixed and purchased that way)
I dipped the end of a toothpick into the VG, then into a packet of Splenda.
I dipped the splenda coated toothpick back into the VG. I did that twice.
I then put the VG with splenda onto the warmer for a couple of minutes, watching it and shaking to disolve the Splenda.
I strained the coffee infused e-liquid 3 times through cotton in a syringe, mixed the splenda sweetened VG into it and shook it up.
Results:
This has potential. I could taste the coffee. I could taste the sweetness (which is what I wanted, to see if I could actually make it sweet) -
But - it wasn't enough to hide or enhance the tobacco liquid I didn't like.
I vaped on it for a while, to give it a fair chance.
I ended up throwing away what I didn't vape. I can see doing this again using Vodka to soak the ground coffee beans. (no PGA here, it's illegal)
Or soaking the ground coffee beans in plain VG+H2O - and adding that to perhaps some chocolate (or other coffee compatible e-juice). Or vaping it alone just to gauge the coffee flavor.
The warmer did help infuse the coffee pretty quickly. If I did this again I'd use a glass bottle though.
All in all - it was fun to experiment and gave me some ideas on how to perhaps improve it if I wanted to do it again.