With the release of the TBC server, I believe this feature is necessary and shouldn't impact Outlands's gameplay as much(relatable to Icecrown with Transmogrification).
My suggestion is to have the ability to Lock XP in TBC. It could be done for 5 coins/points each time.
In doing this, it will benefit some of the Twinks in Outlands (Even though, is the least of the concern of the community), however, it also benefits those who like slower rates by allowing them to lock their XP, do some quests/dungeons etc. and then unlock so they can also get a feel of the Burning Crusade content.