There are several approaches to this problem.
The "bow saddle" is a neat item that works well and looks cool as well. I'm not a big fan of leather grips on recurves but I have used it on some that were just too slick.
It's thin enough that it doesn't change the feel of the grip a whole lot.
A small pad of 100 grit sandpaper rubbed on the grip area of the bow will help with the slipping. Barely noticable to onlookers or in pictures, but improves the "grip" considerably.
Paste wax! A good coat of hard shell paste wax (you've got that around the shop for protecting arrows...right?) Coat the grip area and buff or not. It works great either way.
This is only temporary and will need to be reapplied from time to time.