I would have thought keeping them on the dry side would be better over the winter

I agree with pellie-grower.

The keeping them going in that fashion is an aceepted way...and you might expect them to be leggy owing to the low value of the sun.
Just cut them back as needed. This enables the lower sun to give to the lower size of the plant for continued health.

If the plant is growing new leaves, then sure, go ahead, feed the plant minimally. You don't want to push the plant to produce too much with such low sun not doing well by the plant. Normally, you would not feed a plant that is not growing.
Then too, it will need less water if it is not growing.
As new leaves are forming, water according to its needs...let it dry down between waterings and when you water do so always to drainage, then dump the excess.

Your plant will do only as good as the sun will give.
Soon, depending in just how much sun it receives, the plant will lose vigor. At this time, you may decide to put into storage---a cool place in the basement until mid February when it can be brought out again, cut back and encouraged to re-grow.

I should add though if the geranium can be kept going as you suggested it is, then let it grow as it will until mid February/March....then yu can decide whether you wish to take cuttings from that, divide the plant or maintain the plant as it is and re-pot when it can go outside in May.