Fatigue is not all about drugs.

You Said.DRUGS.... "Perhaps the mousedoctor might like to acquaint himself/herself with the benefits of exercise in respect of fatigue, just because you can't 'prescribe it' does not mean that you should have some idea as to where to direct your patients to reap the many benefits of exercise therapy"Link

You are correct that excerise can help, so see elsewhere on the blog for posts by Prof G and see the Jan 2012 MS in focus for tips (Thanks to Anon 12.43-see comments)

I try to ensure that my particular patients get excersise, but they can not tell me if and when they are fatigued, so they are not much use for drug studies, or studying disease mechanisms of fatigue.

If you understand the cause and mechanism you can work on a solution.