[Jonathan Norris]

Thats a really cool idea... I would also have to agree that ball casters would be a better idea then omni wheels.
My main concern with this idea is the torque required to move the center 'module', because most of your contact with the ground will come from those two middle wheels... and if they provide too much friction you may just end up turning the whole body of the robot. So instead of having a crab drive you have your robots body turreted.... with your center two wheels staying put...

To solve this you would have to either program the wheels to turn the direction your are trying to move the middle module, basically running the wheels in opposite directions helping the big CIM turn your center module. Or you may want to use omni wheels over the kit wheels...

This is defiantly something you would want to do some calculations and small prototyping to see if it would actually work, cool idea thou!