Rob, you might have more luck searching in the DIY sub-forum. I've only skimmed through there, but I've seen mention of special liquid sucralose and something called ethyl maltol that can be had from the DIY vendors...I'm sure there are at least a couple other things that could go into sweet recipes for e-liquid. The search function would be helpful in that sub-forum also.
I bookmarked
THIS LINK a while back, and here's a couple clips from it:
Sweetener’s - Sucralose (Most Common) – Better Stevia (Alternative – some say chemical taste) 1-2 Drops per 10 ml or 1% adds strength in flavor and sweetens greatly. (Remember; less is more, start small) – Mostly used in fruits, candy, and bakery flavors.
Other Sweetener Options – TFA Marshmallow- adds moistness and sweetens. TFA Molasses adds sweetness + a trace spice. TFA Brown Sugar Extra – adds sweetness. Some custards and Vanillas have also been used (Also known to brighten other flavors).