Disposable

I'd be afraid a hard-drive magnet would be too strong and would pull apart any glue or lightweight connection you might use. The magnets on my Dahon are pretty modest, and they're screwed into a waterbottle bolt sized hole in the fork. The fittings are spring loaded for a little bit of flexibility. Perhaps you could insert the magnets into a pair of bracelets made from tubular nylon webbing sized to fit the frame tubes you want to attach to. The webbing would be thick enough to keep the magnets from sticking too hard, and be flexible enough to give an ajustable fit. You might have to stitch them onto the frame so the fit wouldn't be too loose, but that would be a pretty easy sewing job.