Allow for negative values when selecting asymmetric extrude. This would allow you to offset the extrusion from the sketch plane. This type of feature is available in Catia and solidworks and comes in very handy at time.
I know that the same result can be achieved in other ways such as creating additional planes and projecting the sketch geometry or creating 2 additional planes and selecting between in the extents option. But all of those methods required additional steps and time.
Doing it the way I suggest saves time.