... have never tried it in a drive cage, but I did do it for my Zalman heatpipe cooler ...
Nice one! My Zalman ZM-2HC1 cooler has been in bits for a week, waiting for me to find what I did with the tube of goo I bought for that very purpose (must check under the bed again!).
When I first got the Zalman I was slightly disappointed, it didn't seem to be taking heat off the drive nearly as fast as I expected ...
... and then I held the assembled HD&Zalman up to the window, and found that where the two alu blocks on each side were clamped together (hard), and where they were clamped to the HD (hard), light was still flooding through the crack as if they weren't in contact at all!
So I figured that maybe most of the heat must be getting to the pipe blocks through the clamping screws, or jumping the air gap somehow, and the cooler efficiency maybe goes way up when you use goo to get rid of (or at least reduce) those airgaps. I'm also going to use goo within the block pair that clamps around the pipes, I hadn't realised how little surface contact they actually make with the pipe ends, or with each other (try the light test!).
I think that the blocks are probably machined to make a perfect fit with the pipes when there's nothing else in the sandwich, but since Zalman seem to use little dabs of rubbery glue on the pipe ends to hold them in place before the outer blocks are screwed on, that little extra dab of rubber in the pipe trench seems to be enough to raise the pipe profile enough to spoil the fit, and leave you with a crack and an airgap between the pair of blocks.
So maybe goo should be considered an "essential mod" for the Zalman, perhaps.
PS: on the subject of the Zalman cooler, I found that with the two sets of sidemount holes, one set put the HD flush with the bottom of the drivebay, and the other set raised it up too high, so that the copper pipes were unnervingly close to the top cover of the shuttle (or actually touching). I'd also had to raise the pipes a couple of millimetres in order to get the blue side-blocks parallel so that they fitted to the drive on both sides, and that didn't help with the top-clearance problem. So I drilled and threaded a third set of holes between the other two, in the two outer blue blocks, and now it sits very happily in the shuttle top bay.
I think the Zalman is a very nice piece of kit, but maybe there shoud be a FAQ or hints and tips page for it somewhere, so that people can get the most out of it.