how do you deal with heavy power cords?

I have some very heavy power cords that won't stay in a wall socket correctly, the weight pulls them down too much. It's even a problem in the IEC receptacle on the back of seveal components (I have used a foam support underneath, but that is suboptimal for obvious reasons). Has anyone developed a clamp or other kluge to hold these things in a socket? Is the only real solution to find lighter cords (and reasonable flexibility would be nice too!).