Limiting WWW redirect to just WWW

It sounds like you're looking for is for the redirect to include the URI, which is something we've seen many times using the redirect command, and would change very little in your case using the respond command:

when HTTP_REQUEST {
  if { [HTTP::host] eq "www.domain.com"} {
    HTTP::respond 301 Location "http://domain.com[HTTP::uri]"
  }
}

In this fashion whatever URI the user requested along with the hostname would remain intact after the redirect.

Colin