For those using the VB4 mod_rewrite URL's, here is how to do it:
http://xenforo.com/community/threads/rewrite-rules-and-redirections-for-vb4-mod-rewrite-urls.5850/
If you're using something inbetween, ie. advanced, etc... then you should change your URL structure back to standard URL's, which are the same as 3.x and use the 3.x to achieve it or change to full mod_rewrite and use the method linked above.
Changing your URL structure whilst still using 4.x is ok, as it contains a built-in 301 system so you don't lose anything. Then in a month or two, after Google have the new URL's completely, then convert to xenforo using the appropriate URL redirection.
I am with you though... I do hope to see something more robust that caters all 4 URL types from 4.x.