The intercooler is a big restriction on the TDIs, some people have measured a boost drop across it as much as 3 psi. An after market intercooler could help reduce this a lot. I doubt there is room to plumb a new one in parallel. There was a nice place selling an upgrade that had a nice write up showing pressure and temperature drop before and after the upgrade.( Found it
http://www.tyrolsport.com/product_in...ynotesting.pdf )
I would go to talk to the people on some TDI forum about reducing exhaust restriction and maybe see if they have figured out how to improve the intake too. (Don't use a K&N style filter)
I would forget about a radiator block as I wouldn't want to risk engine damage. (I've encountered times when I needed as much cooling as I could get)