It'll probably be patched, but apparently if you give unlockable belts to current title holders (IE: WWE Champion) they can defend the main title in exhibition.
Video's description:
By using an exploit involving the unlockable belts, you can defend the four main singles titles (WWE, World, US, IC) in Exhibition Mode.
Simply assign an unlocked belt to a current "big 4" title holder, and then when going through the advanced options, you'll be able to put a title on the line. As one competitor holds both belts, you can choose which one you want to defend. As you can see in the vid, Orton can now defend the WWE Championship in an exhibition match.
360 version shown here, but this also works on PS3 as well.