Remove Percussive Sounds In Sonar?

I'm working on a cover of the song 'Hey Mama' by David Guetta (and a bunch of other people). The song uses a sample of 'Rosie' from field recordings made at Parchman Farm by Alan Lomax in the 1940s. There are two components of the sample, a vocal part and the percussive sound of picks hitting rocks. The percussive sound overlaps the vocal parts in places. On the original track it sounds like David Guetta is able to control the level of the picks transparently. The third time he uses the sample. the picks are barely audible.
What I think I want to do is isolate the percussive sound so I can phase invert it and control its level without causing the vocal part to drop out noticeably. The hard part seems to be isolating the percussive sound, it's slightly different every time. It was trivial to get the sample beat matched with the song in Sonar using Audio Snap, I get a bit of phasing but it's close enough for rock and roll.
Is there a workflow in Sonar that I can use for this?
Maybe there is some way I can pervert the drum replacer to pull it off?
What are the best tools to use?
Thanks!
 

Another possibility is that if the percussive sound is short enough, you can cut it and stretch the preceding sound to fill in the gap.

Agreed! RX4 is incredible. But it is pricey, so I figured if R Mix could do the job, hey, it's free if you own it. And since it seems like this is a one-off issue, then he could rent Audition for a month and deal with it.

So this is why we should all push Cakewalk along the trail to what seems to be rumoured and the pending Wave Editor. They asked me in the survey so now I'm waiting.. I can only run Wave Lab on one computer and whenever I'm away from home and have my laptop it sucks. Ya I could bring my usb key but I'm scared to death of that thing...