[palegreenthumb]

I wonder if it would be possible to take a pipe cutter, and grind the edge of the cutting blade flat, then use that to press the indentation into the pipe?

This one comes with an extra blade, so even if it didn't work, you'd still have a pipe cutter.
http://www.homedepot.com/p/Husky-Quick-R...258905-_-N

Or, just use a pipe cutter to scribe two parallel lines around the tube, the same width as the indent.