vasquo:
Why don't you just edit the library, clone the part, but make the smd pads bigger on the new clone.Another technique, if there's nothing behind, you can put another heatsink pad in the bottom copper layer, and use several vias to connect/bridge the upper and bottom pads.
Also order your boards as 2oz copper.
Yep - I've decided to do this, I've just cloned the packed with the suffix "HOT".
I'm making the boards myself by UV etching, so I'll have a play soon with 1 vs 2oz etches. Cheers 