I've seen this problem on every single 1st Gen PS3 I've worked on. Personally I can't believe it was designed this way and I imagine that it's the main contributor to the overheating problem that these consoles have. It appears they tried to compensate for this by smearing a ridiculous amount of thermal compound on it, but obviously that didn't quite do the trick.
I do the same thing that Erikjan above does. I've found that a business card folded twice lengthwise placed between the clamps gets it to make contact much better.