I bought a cam lock and alas it did not work as I could not get in between the the gears. Here are some home made tricks I have used before you remove the belt tension.
1) Vise grips locking both gears together. This is a bit iffy as they sometimes slip.
2) Tie wrap! Don't be shy with them. Lock that bad boy down and then release the tension.

The intake cam will move the gear down a bit once you release tension.