One thing you may be able to do would be to develop a new web part, but use the unigrid control inside of it, so that all of your functionality will be there that you wanted. If you reference the unigrid control in your webpart and then use it, all you would have to do is set the data or object type throught the code or a property, and then you can apply your transformation through the code as well.
There may be an easier way, but this should work regardless. Im not sure of the effort it would take to do that advanced export on the repeater, so thats why I am recommending this approach, unless someone else has found an easy way of making that happen.