I’ve got a backward-compatible fix for WPCF7 v2.2, check out this patch:
https://gist.github.com/406757
It works with jQuery 1.3.2 and 1.4.2, and doesn’t break if the server isn’t running at least 5.2.
The fix uses json_encode if it’s available, and strips the slashes from the extra settings on save, so jQuery 1.4.2 has validating JSON.