bbwaffle Feature request - Slit offset

I would like to have the slot offset 80%/20% on my pieces. 

I am curious if this could be added as a feature.

Imagine a 20" cube, Cut once on both planes. Currently The X plane would have a ~10" deep slit, as would the Y.

I would like to put a ~2" Slit in My X, and a ~8" slit in my Y. 

Application:

I am building shelves to store Architectural Drawing sets. I want to maintain the rigidity of the horizontal Pieces (shelves), while allowing the vertical elements (dividers) to slot in primarily for convenience.