After weighing this over, talking to my brother and reading peoples posts here and through Google searches I've decided against going this route. As much as I'd like to help, I don't make enough to have $5000 tied up for a year. Plus, the promissory note/contract I've been formulating has become a little over the top and might actually be offensive to a friend... People are right, there is a ton to lose (Money/friendship) vs. little to gain (my friend getting his dream vaca spot a little sooner than later).
So screw it. I just text him the bad news and he text me back "oh no worries kid" so it's over.
As always, thanks for all the feedback CB. TP's to all.