I need to make fondant gems shimmer, so I was going to use gold dust and vodka, but it turns out the bride I'm making the cake for is allergic to alcohol. I know it'll evaporate and she can avoid eating the gems, but just to be safe, is there any alternative to mixing the dust with alcohol?

You might receive advices to use lemon or vanilla extracts. Please read the whole ingredient list as most extracts are made with alcohol. Water might be your best option, it might take a while to dry out though.  Or you can find alcohol free vanilla extracts either online or at specialty food markets (eg Trader Joes). Good luck 

You might be better off buying an alcohol free food paint, if you can find one. Or a spray - just found one by PME that is advertised as alcohol free. Not all dusts will dissolve well in water, so try it with a little bit first.

I remember reading that some have used dusts w/oil (yes, just plain salad oil) with one major drawback - it *NEVER!* dries.  Any touch will disturb it. Since I never tried this I cannot say how bad etc.

As kakeladi said, oil will work or mix your dust with a little Crisco to a consistency similar to oil paint.  But, it does not dry and is very easy to disturb.  If you can get your hands on cocoa butter, it works the same, but does get firm.