Thought I already mentioned this way of doing split omnis on one stand, though perhaps it was on the old Oade board. At any rate, here it is:
A relatively cheap and easy way of running split omnis on one stand, with about a 3' split is to get the Atlas 5/8" to 5/8" female coupler, AD-5B ($4.50 from markertek.com) and the Atlas 31" extension tube, TB-58X ($9). Take your clamp (you do have one right?--well if not get one) and mount it to the top of your stand at the 5/8" stud side by using the AD-5B coupler. This will leave you with your stand with a clamp attached at the top, with the clamping portion of the clamp unused.
Take the 31" extension tube and attach it (horizontally) to the stand by inserting it into the clamp and tightening the clamp to the extension tube. You've now got a 31" spread for your mics, and the extension tube already has the correct 5/8" threading on either end. Attach your shockmounts or mic clips to the extension tube, and by now you've got a 3' spread or so for your omni mics.