For your beater bike, I say hit the electrical department next and try going nuts with the conduit. They'll usually have benders to use in store. I'm imagining two 90deg bends in the middle of the piece to form a semi-rectangular platform end that could mount to your seat stays somehow, then two 120deg or so bends where the platform ends return downward to connect to the dropout. Zip-tie a crate to the top to give it lateral rigidity and carry capacity. Whatever you do, never weld conduit, it'll poison you.

I've got a bit of a DIY project to organize my garage. I'm hanging all of my and my wife's bikes on the wall, leaving about 3 ft. open below. I'm going to mount some heavy-duty 20" shelf brackets and bolt a length of 1" conduit to the end of the bracket and cover in somthing to prevent scratching, all about 2ftoff the ground. I'll use it to hang my kids' 16" bicycles and their Big Wheels from the front wheel. I'll post pics when I get 'er done.