for stuck fermentations, go with ec-1118 yeast, it's pretty much the best one at restarting stuck meads, in my opinion. i am a huge fan of cyser, so i say go for it.
what i would do though, is take your half gallon of stuck mead, and dump it in 2 gallons or so of apple juice. maybe even 4.5 gallons. that way it won't need to age anywhere near as long and it will be a delicious cyser.
this is probably just my bias against batches smaller than 5 gallons though. it would definetly be easier on the yeast to not pitch into alcohol that is that high.