Island Mist kits are made to replicate a cocktail, not a true wine.
SWMBO and I discussed how we planned to address this issue. I suggested adding a few pounds of fermentables, but she was not entirely excited about the way that would throw off the acidity, etc. (She has a lot of input in wines... couldn't care less for beer brewing, lol!)
We decided that at the end of the fermentation and whatnot, before bottling, we would dump a bottle or two of vodka into the mix and then bottle after that. We're going to use a flavored vodka that will "match" the Island Mist flavors.
How will that work out?
23L * .06 = 1.38 L EtOH in Island Mist
1.5L * .40 = 0.60 L EtOH in 2 bottles of flavored 80 proof vodka
1.98 / 24.5L = 0.08 = 8% ABV
At low volumes, each fifth of 80 proof vodka adds about 1% ABV, so you can substitute your own numbers in there and figure how much you need with some algebra (the 1% ratio isn't constant all the way to 23L). It's not as cheap as sugar would have been, but I trust that it will work out very satisfactorily in the end.