To be honest man if you want to make legit Demos then you'd be better off either doing it in a single take or using some editing software. If you're internet savvy and familiar with getting things free I'd highly recommend Vegas Pro, it's so easy to use and is top-notch.
I rent 2 shitty ass cameras & tripods from my school once in a while to make a simple 2-angle demo (pedal view and guitar view) and record into my computer interface. It's a bit of work but it gets the most basic quality across. Here's some examples of mine if your interested:
http://www.youtube.com/JacksGearDemosAlso you could probably practice for a while before so you can nail it in one take if your really good. Also recommend doing a test recording at different volume levels so you can find out which one works best.