they make plugs that are tapered just like the flare on a normal brake line. i know napa here in town had them in stock when i needed a couple. you can they the "fold over and clamp with vicegrips" technique but i couldnt get it to seal at all.... and just like was said before, dont drive it more than needed and take it nice and easy. i would *never* try this on a front brake line but on one of the rears you probably wont notice much difference. just take it easy on it though.
you'll probably have to bleed that line too, just crack open the plug just like you would a bleeder screw if you were bleeding the brakes under normal conditions.
oh, and no, you cant use just a bolt. brake lines seal on the flare, not on the threads. thread tape or sealant wont do you any good either.
crap... just read the part about not being able to get to a parts store.... i dunno about that one man, i wouldnt risk it if you cant do a decent repair. not having rear brakes is one thing but leaking brake fluid is something totally different.