I have one done and yes I broke a switche before finding out how!

Depress the tabs on the side and gently lever the switch rocker out from the front.
Use your broken switch as a map for the wiring - I
think the terminal nearer the edge of the switch is earth but double check that.
It will be a PITA to find a route for the resistor to fit in but it can be done.
You will need much smaller LED's - 3mm IIRC
Good luck!