Join date of 2006 and your first post is 2011. Wow! Hope you have been lurking and learning all that time.
I have had both front door panels off my Chevy but there may be subtle differences between my Trailblazer and your Envoy. However I am sure I am just not on the same wavelength as you. The way I am reading your question my answer would be to remove the other bolt(s), loosen all the clips, and remove the door panel so you can access the broken bolt to remove it. Buy a new bolt and re- assemble. What am I missing?
Can you post a picture of the broken bolt?
There is an article in the "How To" section about replacing side view mirrors with mirrors that have turn signals in them. That article mentions removing the front door panels and has lots of pictures..
There are on line retailers of GM parts and they have exploded views of EVERYTHING. Perhaps you could look at one of there site to see what parts are available indivually and what parts are only sold as a package. After you figure out how to take your door panel off there is always the option of getting a replacement from a salvage yard.