revo slipper in e-maxx tranny retaining 1st gear?

Hi,
I have read someone modified the tranny with revo slippery with single tranny.
I would like to ask how to do the same modification with both 1st and 2nd gears retained.
What I think of is to drill a new hole for the first gear.
It could be a mass in the drilling work for me.
Any other better solution?