I usually remove the wiper, which leaves just the post with a rubber surround usually. I tape up the perf in place, and where the post sticks in to it, I cut a small hole, or just mark with a Stabilo. Then I measure the rubber trim around the wiper post, and go back to the table with the perf and cut out a circle around that mark or hole I made. I have a circle cutting tool that makes a perfect circle. Then when installing the perf, it fits perfectly over the wiper post.
Simply slicing a 'relief cut' looks unprofessional and leaves something that can peel up later due to heat, moisture, etc.