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Andrew Straw said more than 17,000 eligible US voters lived in New Zealand.
Although the voting deadline had passed in some states, such as Florida and Illinois, the deadlines differed according to state, so there might still be opportunities to register.
Mr Straw said the Vote From Abroad website allowed Americans living abroad to download and print out an absentee ballot, which could then be posted or faxed to the relevant address.
A University of Otago international office spokesman said there were about 500 US students on campus, along with several American staff members.
In his spare time, Mr Straw is a volunteer for Democrats Abroad.
Along with posting messages on public noticeboards, he contacts people en masse using emailing lists and social networking sites.
The Internet made it easier for Americans abroad to follow issues.