I have to admit that I was somewhat envious when I read your post. You are so blessed to be able to have "the best of both worlds." A "booby prize" is not really my style, so I don't know what to say there. However, since you seem to have a close working relationship with this people, I'd recommend a humorous thinking of you or thank you card with a gift card to/for something they enjoy. (If you can't find a card you like, most pc/office computer software comes with some type of program that would allow you to make your own card.) I do this for invitations to my children's events all the time. You're Invited...with the child's photo on the front. In your case, Thank you...with a photo of baby on the front, and then a brief not of explanation inside (that could be typed in a neat font or handwritten.) Good luck!