I got this idea from a co-worker a few months ago and finally tried it out in my bootcamp class this AM.
Play the song "Roxanne" and do a plank the entire length of the song. 3:14 is the length I had. Then when you hear "Roxanne" do a push up and right back into plank. I believe there are 26 Roxannes in the song.
Try it some time and enjoy!!
I did this with the bootcampers this morning and it was tough.