Unfortunately, there are only so many options for preventing fermentation in sweet wines and they all involve some degree of sacrifice or difficulty. The list of “cons” is long compared with the one “pro” of an arrested fermentation. First off, you’re correct that adding sorbate can sometimes produce off-flavors over time. Secondly, fortifying with alcohol to a point high enough to retard refermentation (usually around 18% alcohol) is not ideal for all winemaking style goals; you’d be better off aiming to make a Port-style wine in the first place. Thirdly, it’s impossible to add enough sulfur dioxide to ward off fermen-tation without compromising aroma. Who wants to drink a wine that smells and tastes like sulfur dioxide? And finally, filtration is fiddly and, if you have to buy or rent the filter, can be expensive.
So what’s a winemaker to do? Depending on the volume, and especially if you have access to a second fridge in your house or cellar, did you think about sweetening it and then chilling it? I’m thinking, especially if you saved it for a major celebration or holiday where you and your guests might conceivably go through a whole carboy (or two?) within a month or so, you might be better off to sweeten it, chill it, store it and drink it all without going to the bottle at all.
Barring that crazy thought, I think you should give potassium sorbate a try as it seems to be the least onerous of the options. You may get lucky and perhaps won’t experience much of the “sorbate off-aroma” that can smell like geranium. Unfortunately, you really can’t do bench trials on 100 mL samples like I usually recommend, because the off-aroma from potassium sorbate happens in the bottle over time as the sorbate is broken down into ethyl sorbate. However, you can try to limit the amount you put in. What’s nice is that the higher your alcohol, the less you have to use. For a wine that’s 12% ethanol, a recommended dose is 100 mg/L, while 10% alcohol wine needs 150 mg/L. Adjust accordingly. The silver lining here is that the off-aroma may not develop, or that the fruit quality of your wine may be able to tolerate it well. Other than turning your wine into a fortified product, or filtering, I think that’s perhaps your best avenue.