Constraints IPOs (keyframing influence) - how?

I have two bones, one on the left side of my character, another one on the right. Each of them has Copy Location constraint. At the frame #1 I need for the Influence of each of the bones to have 0 value. and let’s say at the frame #5 I need for left bone to have influence 1 and for the right one - 0. I pressed “Key” button right next to the “influence” slider. Then in IPO window I chose “Constraints” and I saw my IPO curve. The thing is now that curve controls influence of both bones and I can’t figure out how to have two IPO curves to control left and right bone independently.
How can I do that?