Muppet? It's a legit question IMO
It has actually been done a few times, but it's a Lot Of Work. The engine mounts of the Golf are different, so that means fabricating and welding new mounts inplace. The Mk5 Polo Tdi (3-pot) should actually fit, but I bet those engines are still quite expensive. AFAIK, that has not been done before. The engines from the Polo Classic or Variant (Estate) have the same mounts as the Golf range.
Also, I've heard stories about the 4 cylinder TDI engine being too high, so that the bonnet won't shut and/or the oil pan scrapes. Don't know if that is true or not though.
The electronics is more or less the same as with any inter-model conversion, so hard but doable.