I always use copper mini-heatsinks from Enzotech, they are very good at dissipating heat from mosfets, about the right size also.
Lately I've switched from them because now Watercool makes a DIY kit that watercools mosfets too on universal waterblocks.
It's a very nice solution, you just cut the copper where you need it to be and drill couple of holes matching near the VRMs.
Then you proceed by connecting the rigid tubing with small push fit fittings.
BAM watercooled VRMs on universal waterblocks.