Today Ion "Watcher" Hazzikostas announced that the patch 5.4.2 PTR is beginning testing for exactly that feature. This process should allow players to move heirlooms between servers, in advance of the changes already planned for Warlords. The feature should work like any other cross-server communication, in that instead of simply mailing to a character name, you would be mailing to "Charactername-Servername." Note that this feature is only for account-bound items like heirlooms -- mailing gold or other items won't work. Players wanting to test this feature should hop on the patch 5.4.2 PTR and mail account-bound items across servers, reporting any hiccups by bug reports or feedback. For more information, check out the official thread on the forums -- and look forward to being able to chuck your heirlooms to your alts in patch 5.4.2.