I must admit, I haven't encountered the problem, but I jump alot though... it's just.... so addictive... bounce bounce bounce...

Anyway, if it's slash commands only that dont clear afk, and "normal" spells from your spellbook does, you could just hit watershield every minute or so (no reason to make that into a macro)

I'm running my warlocks mainly now, so I haven't checked on the shamans... and can't check this from work