...of course it will limit you to FW800 speeds. Also bear in mind that it will only support "direct connect" esata devices, which from what I understand rules out most devices sporting both USB & eSATA connections. I don't really understand why, but that's what Firmtek told me - "It will not work with hybrid enclosures that include eSATA/USB and/or FireWire".
But the general answer is... you can't. One of the reasons why taking the expresscard away was a really dumb move, if they wanted to get rid of expresscard they should have at least added an esata port, but with Apple that seems unlikely ever to happen.
Yes - they still have express card ports on the 17" models only. I really do wonder why none of the other models omitted an eSATA II connector. It seems very silly when you are working on a pro line of computer!