You can get enzymes to assist with fermenting the carbohydrates.

Also is is usual to allow potatoes to start to sprout before fermenting them (for wine). When they sprout, the natural enzymes have already started to convert the stored carbohydrates to sugars which the plant needs to grow.

I'd do a bit more research on potato wine and consider making up a batch - it is an interesting drink to say the least ! Aim for a semi-sweet style IMO.