+1
Even though your prescription is for multi-focal glasses, shaving is done at a fairly constant distance. As long as you don't also need a major correction for astigmatism, etc, a pair of drugstore readers of the desired strength may be all you need for shaving.
A magnifier mirror isn't a bad idea either, and you can also get them with battery-powered heating elements build in for a fog-free shave.
If you have complex prescription with multiple corrections, you can ask for a task-specific set of glasses.