The only potential lead toward making a solvent based version of dithionite is dithionite dissolved in triethanolamine. There's a patent about dithionite being preserved in it. In actual usage it does work to some extent, but far from perfect. Fresh mixed when mixing the solvent with equal part water will make film darken to black almost instantly, but after 1 week in refrigerated storage (note my TEA is low freeze grade, so doesn't freeze at a temp of around 40F) it'll only turn a dark brown after a few seconds and takes a while to turn completely black. This might still be close enough for a fogging developer though if you account for the imprecision with additional time. After 1 month the solution was still active. It seemed like it decreased in activity a lot over 1 week, but afterwards the activity level seemed fairly stable for 1-2 months. I only tested this once though so take with a grain of salt. I can't find my notes for how much dithionite I actually dissolved