I think this has actually happened a few times over the years. I remember once in the late 90s, Bob let an older gentleman who played the harmonica take them to commercial, and I don't think the regular theme ever started. Also, when "freak dancin' Mitchell" won Barker's Bargain Bar in 1998, the "freak dancin'" music returned and took them to commercial. Also, I've seen a couple of other occasions during the 90s where the theme for the prize would start up after the contestant won, rather than the regular theme.
I hope I'm reading the original question correctly and not giving an answer that isn't being asked for.
EDIT: I think the original question is asking on a "regular basis" type thing. Oh well, I thought my comments were interesting at least.
