OK thanks, I think I've got it cracked now... I hadn't realised how you could change your own speed using events... DUH. I will report back my success. Thanks all!
UPDATE: Yep, I got it all working now. It's kind of a strange way to do it, but you 'activate' run mode by using an item. this toggles run mode on/off. It may sound clumsy, but it works well in practice.