How do you demonstrate performance in paired-programming environments?

Question

Performance reviews have come up recently at my work, and I was put in an interesting position. Our team does a lot of pair programming, which has a tendency of averaging out the skill differences between team members (especially considering we rotate pairs). Generally, when doing performance reviews, you look back at the work you've done, and demonstrate what you've accomplished, and how you've exceeded expectations to try to negotiate a raise or other benefits.

How do you demonstrate (or even measure) individual performance in an environment like this?