I spent some time in your city back in the early 70's.
I have changed mirrors on bikes a couple of times. But not on a wing.
So I hope someone jumps in with Wing knowledge.
Anyway for Bike mirrors, I have replaced both a a Venture Royal and one on a V-Max I owned.
First form a heat barrier wall using Cardboard or anything you can use to put between the mirror and the plastic housing.
I used thin cardboard like from the back of a writing tablet and had it inserted all around the glass, Between the glass and the mirror housing. This will help protect the plastic housing from heat from your heat gun.
Now I have heard of people using their wives hair drier. But in my experience the hair dryer does not get hot enough.
If you do have to use a hair dryer, Cover some of the holes that let air flow in and the hair dryer will get much hotter. Make sure you uncover the holes before you sneak it back into the wife's drawer. grin
I have also heard of people using a butane torch. But I never had balls enough to try that.
I used a Heat Gun set on a lower temp and creep up to a higher temp if needed.
Now play the heat gun around the surface of the mirror, spending more time in the center of the mirror.
Now this is the Cool part about using cardboard. If your pieces of cardboard are fairly stiff they are acting like a wedge by being stuffed between the glass and the plastic housing.
When the adhesive that is holding your mirror gets hot enough the mirror will just pop off the mount and you can then lift the glass free.