I just picked up a set of Phottix Stratos II flash triggers. They have "pass-through" eTTL, so you could put the transmitter on you camera and attach the ST-E3 to the top of it. Your ST-E3 should work exactly the same, but the Stratos will wirelessly trigger your remote flashes (you'll have to have the remotes on the Stratos receivers).
I just bought my first 600ex and already have 3 580s, so I wanted to see if I could find a cheaper solution than upgrading to a few more 600s. I used a set of Stratos triggers (1 transmitter and 2 receivers) this weekend and couldn't be happier. They are very compact and worked flawlessly. After suffering through a few years of abysmal performance with 4 PocketWizard Flex5's, the Stratos are damn near a godsend. I can now replace a $1,000 useless investment in PWs (not to mention $75/ea to get my 580s modified for RF signal noise) with about $200 in Stratos and I actually have more capability with these. The only loss is not being able to have the remotes use eTTL, which I never did anyway.