I know exactly what you are talking about as well.
What you can do is to cut back the rock on the side you want to trim. Then glue up a 3/8 x whatever width you need to the outside edge of the jamb clamp and sand.
You can also nail packers directly to the face of the jamb, but then you will also need one behind the outside edge of your pilasters. That may put you into all your light switches. It will also change the look by adding an additional inside and outside corner to the base and crown per pilaster.
I wrote an article in '96 for FHB which was very well illustrated by their artists on using this technique among others to do wainscotting jobs on the cheap. I was making my own jambs, so I made them the same widths as the studs. That way I could just nail the packers onto the face of the jambs with a 1/4 reveal.
That article is still for sale on the taunton press after all these years. Actually, I think it is probably the best article I have ever done.
I can't get to the article because I don't allow cookies but it is the third one down on the above page - the name is jim chestnut. There is a picture on the front cover of the mag that issue that will show what you are after. There is also a pic with the article as well. You may be able to get to a pic without having to pay 3.50 to download the article.
What you are doing, by the way, if you did it the way I described, can eliminate a whole lot of problems associated with pilasters, plinths, pilaster wraps etc. It will allow you to use standard doors, for instance, where the bottom hinge positioning will not interfere with tall plinth blocks.
You can run into the same problem you are having with some factory door when using nothing but casing sitting on a plinth block. You have to hold the thick plinth back far enough so the hinge won't squeak on it, but then when you center your casing on the plinth, you run out of jamb to nail the casing - same problem your are having now.
By doing what I am saying, you can lighten up the design and de-formalize it as well, by using base wrapped pilasters to just under the chair rail cap. Wrap the bottom of the shortened pilaster with base and cap at the bottom, and run the chair rail over top of the pilaster and returned to the packer. Then you can set the actual casing on top of that chair rail "shelf" and miter the top corners of the casing.
The result is a less domineering look than what you get with full pilasters with a crown wrap at the top.
Doing what you are doing will be well worth the effort in my opinion.
If you are not yet confused enough, do not hesitate to reply. I'm sure I can get you even more confused without even trying very hard.