One of the best things I ever got for DS is an Ipod Shuffle. He is non-verbal but wanted the same music over and over. We tried to reduce/eliminate the behaviour but without success and it was driving us mad on car journeys. Maybe something like that would distract him? You could download spoken word progs and stuff about anything he is interested in (or obsessed with).
Yes the repetition used to drive me potty as well and on a bad day (his - when he is so yonderly he is not really with us) it still does. However, it does improve and now he only really goes on and on about things as I say on a really yonderly day. Otherwise he is pretty ok now - a bit repetitive (about the bloody cats on holiday) but not nearly as bad and doesn't seem to HAVE to ask me the same question six million times which he used to do. Still repeats when anxious and in social situations though.