Gar hit the nail on the head with the very first suggestion.
I know you have probably already bought something for your artist, and likely shipped it... but yeah, a Nerf (tm) gun along with a target to shoot at would be ideal. Something to provide a bit of fun distraction, but not so distracting as to stop him or her from working. Great idea.
Artists, like any creative types, already have their preferred supplies and media. Buying tools or supplies for an artist is like buying clothes for a friend, they'll smile and say thanks and then toss it in a corner because it's just not their style. Simple fun is always good.
That is, unless this person has a wish-list of items you could shop from. But if they did, you wouldn't be asking, right?
