Sometimes you can get by with using the clone tool (rubber stamp) and in the top toolbar set the "mode" to darken and the opacity to about 35%. Then use a soft edged brush to paint the glare off. Occasionally, one eye won't have glare on it and you have something to work with "borrowing" that eye and doing a horizontal flip.
The sneakiest way is to take a shot of the people with their glasses off and switch the eyes over into the glass frames. Whenever I have someone in the studio, I take at least one shot without the glasses so that i have some unobstructed and unglared eyes to work with in Photoshop.