...
I have a cheesy cheap yamaha keyboard PS-303E or something like that, and it has a feedback setting that to me, sounds pretty dang just like really nice guitar feedback. Maybe there's a midi or computer-version you can do that is like that keyboard effect. I've been wanting to throw it in a song somewhere.
Otherwise, I'd do what you need to do direct, and then if you do have an amp, just wait til the house is empty and do the feedback on another track with a real amp separately and blend it in in the mix.