The sidechain in the Live 6 compressor is only a sidechain EQ: the key signal is still the same than the one being compressed, but it goes through equalization first. There are some important uses for it, but in this case, it's not what you're looking for.

The kind of sidechaining you want to do is compressing a completely different signal (a significant part of the whole mix) according to level changes in a whole another signal (the kick track). As has been pointed out, Live 7 has a true separate key input in its compressor, which does the trick.

However, Live 6 itself is totally sidechain compatible, so any plugin which has a real seprate key input can be used in it. You have no need for the mentioned Sidekick plugin, as that one is intended to provide you with workaround sidechain routing in an environment where it isn't supported in the first place.

So, all you need to do is to find a nice compressor with a real sidechain key input. Then you can (for example) use the effect returns in Live 6 to route a signal as the key.

Here's a free one I have previously used successfully quite a lot: http://www.kvraudio.com/get/1315.html

And here's a very nice commercial one (but not expensive): http://www.otiumfx.com/compadre.php

And then of course, there are other reasons to upgrade to Live 7 than just the sidechain enabled compressor, so... Your call. But I do get what you mean by not messing things up doing an upgrade in the middle of a project. In the mean time, you might very well get the sound you're after, using the free option I linked above.