I was thinking I would allow it in a second. They only get one domain spell per day, and most of the domain powers arn't that powerfull. I can't think of any that are gamebreaking. Strength and Travel are cool domains, but I would allow either in exchange for a feat. Without changing the mechanics, but changing the explanation of the source, I could see allowing those to a figher or rogue in exchange for a feat slot.
PS, sorry Bront. It sounds familiar, but Don't remember where I saw it.