You cant... I mean its really hard, time consuming, RAM/CPU consuming and at the end you will have a big headache instead of lightsabers.
I suggest you to try AE. Andrew Kramer has a nice plugin that allows you to make easy lightsabers with many addjustmens :)
Just remember. desaturate the green first and then apply the yellow.
Or just do the awesome way of Davnes007 that he keycorrect the saber :D
-Angel