It makes total sense. You could also garage the heart in there while you make the spacer. That way, the mandrel doesn't get too hot to hold.
I just tried to make one yesterday and wasn't fast enough with my spacer... garaging the heart would keep it from exploding like mine did. I just don't play nice with soft glass. I like boro, because it would have been just fine. I also have a hot plate I use to keep pieces warm.