To do this i usually try to reverse engineer the kick drum back out of the loop. With that i mean to try and undo what the engineer might have done.

Simply put,
1)the engineer would have allowed the kick about two freq ranges (usually around 0hz-150hz for the bottom and 800hx-3khz for the click).
2)He would have mono'd the kick samples channel so add a stereo width plug-in (I use S1 by waves usually) and try and eliminate a little of the kick by taking out a little of the centre most stereo image. If this is causing to much change to the vocal give up right now as this step will not work any further.
3)If the loop has been compressed in relation to the kick (Sidechain/production or mastering compression) play around with a good compressor/expander to flatten the loop out. If this is not working I like to compress the living hell out of the sample untill it sounds like it has been splattered on some invisible glass infront of my face.

If that all fails try and find a sample of the kick drum on its own on the record and sample it aswell. You simply have to layer both samples so the kicks are perfectly in time (using something like wavelabs montage feature or cubase/protools/or even fruity) and then you phase reverse the isolated sampled kick. If you have lined it up correctly both kicks should dissapear as soon as you phase reverse it.

Hope that helps ;)