Wheeeeee! Not my favorite show in the world, but Bamber-Griffith babbies gotta eat. XD And until he has a new regular gig why shouldn't he be a professional guest star? DEAR TELEVISION: ALL THE GUEST ROLES. GIVE JAMIE. KTHX.
Since it's just a one off, he didn't want to make a big deal about it.
Oh, silly man. One of your one-offs is worth 20 of lesser beings. Go on, though, keep being modest, that's what we're here for. To tell you "Silly man."