Cooling for D2PAK dissipating 30W?
I suggest that if none of the 'standard' approaches work that you should look into one of these power peg thermal connectors.


(from here, also here and here)

They're by far the best solution I've seen for thermal management of SMD parts, but I've never had the need for them so haven't prototyped with them. 

(No affiliation, just remember seeing them a while back)