How can I install these pre-hung doors?
There is no reason that you can't make jamb extenders these are routinely used in prehung windows. The casings and whatever you use to bridge the gap to the jamb are just trim and have no structural component.

The trick is to avoid using the exact same thickness. When two pieces are meeting in a plane, it is best to have a slight reveal, an offset (usually between 1/8 and 3/16 inch). This way you have an intended step, not an almost exact match (that is never quite exact).



You can glue the edge of the extender to the edge of the jamb (maintaining the reveal) and pin the face of the extender to the underlying stud.

Most stock prehung doors use jambs that are 4 9/16 inches, wide enough for 2x4 framing (1.5x3.5 actually) and two 1/2 inch drywall faces.