Stabilize and use the top-up as a little bit of backsweetening.
I ferment in a bucket and make sure I've got plenty to get up into the neck of the BetterBottle. When I rack, I normally have to add under 4oz of fluid to get back to that level. So I've never much cared about fermentation taking off again. It will ferment out what I've added, but at that small amount, the yeast in suspension will do it. It will prolong clearing a little. But not much.