This is out of my experience. I suggest you post in the Tweaking Cheap Kits thread for better help.I’m wondering what adding black grape skins from the grocery store would do (possibly after I juice them and use just the skins).
My take at this point -- you're better off buying a better kit, bumping the OG up with sugar to 1.110 - 1.115, using EC-1118, and step feeding the wine until the yeast quits. Bulk age at least 6 months, then backsweeten if it needs it, and redo the Everclear calculation.
I'd do a limited experiment -- move most of the wine to a 19 liter carboy, and experiment with the remaining 4 liters. Once you've fortified the wine, it will probably need at least another 6 months aging in the bottle before you know how successful the result is.
This contradicts some of my previous advice, but you're comfortable taking some risks (as per your initial post), so go for it! IME, trying to go cheap on something like this will not produce the results you want.