You'll have to buy a 4 continent and return by Asia. You're not allowed to recross oceans.
Excerpt from Fewmile's OWE site:
133N ROUTING/ 1. TRAVEL MUST BE VIA THE ATLANTIC AND
134N . PACIFIC OCEANS. ONLY 1 CROSSING OF EACH
135N . OCEAN IS PERMITTED. TRANSOCEANIC
136N . SURFACE NOT PERMITTED.