It cracks off just the same.
David, you be hard pressed to get even a hot soft glass glory hole to do what you want. No reason you can't experiment though. You could theoretically use a soft glass collar but it would slip right off the pipe before the boro started moving. There's a lot of other little things about working boro out offhand. With a soft glass background you will find what is usually up is down and vice versa. But, generally speaking, it's all glass and kinda works the same.
WWUD? Think for yourself.