Unles you really know what you are doing, and are familiar with the room you are using for the recording, I'd give up any idea of recording the reflected stuff and go for adding some reverb etc. post-recording if you're not happy with the "live" sound.

Given that you've not enough tracks to mic each performer separately, and can't get accoustic isolation between them I'd say that your original idea of how to mic them is probably the right one, but not with SM58s.

Also - remember that if you close-mic the pipes you'll have to mic the drones separately.

G.