Tickets are generally valid one year from date of issue (or is it travel).

Are you sure he's not going to come back at all during that time?

You could either:

1) Book a cheap return with a date in the year time frame. You might be able to keep moving it.

2) Book cheap return and throw away return portion (cheaper than a single - maybe).

3) Check with a specialist travel agent like STA Travel (who specialise in students). They may have something for you. And maybe even a bigger discount My friend's son went to NY last year and the STA ticket was flexible and he could change it. A normal BA cheapie wasn't changeable.