Adding more yeast won't help unless you have no yeast in there, yeasties reproduce on their own.
The secondary can go slow, things to speed it up:
Temp change (warmer better)
Yeast energizer (not worth worrying about at this stage)
Adding oxygen (not worth doing/necessarily safe at this stage)
Bottom line is what is your definition of slow and what's it at? not all wine ferments far under 1.0, it could be just about finished. When it stays the same for a few days, it's done.