another fairly cheap solution is to replace the power supply with something beefier.  my personal recommendation (and what I did for myself) is to spend around $150 and purchase 2x of these 750w kits - http://www.gekkoscience.com/products/server_supply_breakout_board.html - and run them with power sharing pins and you have more than enough for the S2 (unless we figure how to overclock past 250mhz) and enough for 3 overclocked S1's.  and if you have one of these power supplies go bad you can replace it for a cheap $25 from ebay.  i keep an extra few on hand for myself anyway for rapid deployment for myself and customers.  if you want more info on the maker of these you can read this thread - https://bitcointalk.org/index.php?topic=379677

DISCLAIMER: I am in no way affiliated or compensated by sidehack for this recommendation.  he has a decent product and i feel he should make money for his work and research.

EDIT:  here's pictures of my setup
https://dl.dropboxusercontent.com/u/23772269/2x%20power%20supplies%20in%20tandem.jpg
https://dl.dropboxusercontent.com/u/23772269/top%20view%20case%20off.jpg
https://dl.dropboxusercontent.com/u/23772269/top%20view%20with%20case%20on.jpg