i proberbly just use it as a tarp/basha.
i never had handeld a disposable poncho, but maybe you can take round rocks and put it in the corners and make a knot in it so you can use it to attach the cord. Not sure what i would build, but i will use a site were you are reasonaly sheltered from the rain and wind by nature. Construct some something with the poncho's, maybe a flying diamond, if possible( a poncho looks kinda small ). depending on the surroundings. Or i can build a A frame type of tarp with the 2 poncho's ( 2 lean-to's facing each other ? ) and close one open side using branches, which i can saw or breake to the right size and cut a sharp end so i can secure it beter to the ground.