Thanks loula, that's actually a great idea! Hadn't thought of that at all.
For Christmas, all he wants is running gear for next year, so I'm trying to get some inspiration beyond the usual (really nice tech top & lyrca, belt, books etc etc) and the arm things are a great call for the early months. It's the Isle of Wight race he's doing in June, which could be pretty warm, but should be easier as it's got support along the way I assume..!