A glue gun is the perfect hot air gun, 1 because its shaped like a gun, and 2 because the back in the entry for your airline and the front is the heater, not extra extension coming off the top like that hot air pencil mod. This is a concept right now, mainly because I just haven't gotten the parts yet but none the less this still should be a relatively easy project.
Step 1: Supplies
You will need:
1. a glue gun (any will do; you can probably pick one up for
about five bucks at some craft store)
2. desoldering braid
3. hose thin enough to fit through the glue stick feed
4. something to go between the plastic and metal to prevent
it from melting (i'll think about this one and then get
back to you with something; rubber is a possible solution)
5. a metal coupling to hold the hose in place, or some heat
resistant adhesive (now that one I don't have an answer
6. some sort of air compressing system. the aquarium filter
as a source of air seems a little to bulky, so look around
for a water pick and use the thing inside of that. you
could probably mount it for more portability to something
like your belt. (i will have pictures of this soon)
Step 2: Reference
Search digg or make for the "surface mount soldering" stories, and you will eventually end up at endgadget. this is just as good as any of the other ones, because they are all the exact same thing. you might end up at a site about a pencil tip hot air gun as well. in these articles, just follow their instructions on how to modify the tip which should be the same for the glue gun's tip. if not, go out and buy a different tip or use common sense and compromise.
Step 3: Assembly
it's really just as simple as assembling the parts in a logical way. first, attatch the hose line to the insulation, and the insulation to the very entrance point for glue sticks. then, attatch the other end of the hose to the air feed assembly, whatever it be that you decided to do, and then fire it up. it should work just as well as the pencil hot air gun mod, and if not, then use it to melt the glue off of circuit boards. otherwise, modify it to be more like a soldering iron and up its heat output.
Step 4: In Conclusion
Now while i know i say conclusion, i will come back to this instructable and finish it. I am really sorry about the obvious lack of pictures, and when it's not 5 AM in the morning, I will do this project and fully document it, and then repost/revise this instructable to be easier for you. If not, then someone else can do it for me.
For all of those who want to do it right now, then i wish you good luck.