They did manage to send Enterprise and 747 on a European tour in the eary 1980s, so the Atlantic can be crossed without unmanageable hops. IIRC, a version of the Mate-Demate Device (i.e. the big gantry) can be disassembled and fit into a C-5. Easter Island was the most interesting alternative site, because it's an awful long haul to the Chilean coast.

One big factor in the geographic distribution of emergency (prepared) sites is that most such landings would result from problems immediately after launch (engine out at just the wrong time, for example), which means there wouldn't be much need for sites south of the continental US. And Easter Island? That dates from the time there was still plans for poar-orbit shuttle missions launched from Vanderberg Air Force Base on the California coast, headed south over the Pacific.