I did something similar to the above, but with the center in a spacer block attached to a scrap piece under the baffle. I cut a rough hole with the jigsaw first, then used the router to remove the last 1/8 - 1/4" and finish it to the final diameter. Also, I only did this once. That is, I made a template out of 3/4" MDF with a nice hole in it. Now, I just attach the template board to my baffle (with rough hole already cut) and route it with a 1/2" top-bearing pattern follower bit.