Well, yesterday I finally got to watch the tape of Don's appearance on Jeannie. Was this 1966? I'm thinking that was the year.
In the version of the episode that appeared on TV Guide, Don appeared only in one scene, as one of three air force officers interested in courting new "secretary" Jeannie Jeannie.
Don did have a couple of lines, but appeared in long shot throughout, and most of the time, his back was to the camera. There was a nice moment as he was exiting where he flashed the Larry Hagman character one of his gorgeous smiles (we didn't get to see those very often on DS--I remember one he pulled on a fade-out in a scene with Grayson, where I always think she was sticking out her tongue at him, or making one of her outrageous faces).
Thanks again to John for alerting us to this. It was great to finally get to see it. I had missed several previous broadcasts.
G.