I have an older Choate pistol-gripped shoulder stock that I had on an 870, and had contemplated doing the same thing, to it.
In my old Choate stock, there are brass 'inserts' in the plastic (that use machine threads, instead of the buttplate screws going into plastic.
I'm not sure about the newer ones.
I was going to take the stock off, wrap it with masking tape, mark/scribe where I was going to cut, then use a Radial Arm saw with a fine-tooth blade, then epoxy some plastic into the stock, for inserts/screws.
Care must be taken to ensure that you keep the same angle/dimensions as the original end of the buttstock.
Did I cut my stock. Nah. Wasn't worth the trouble.
That old Choate Stock is in a box, in a drawer, in my workshop, taking up space.
IF you choose to cut your stock (for the 1100) "measure twice, cut once." There is a spring assembly inside the stock, and the 'screw/stud' that attaches the stock to that spring assembly.
Don't cut the stock so short that you can't secure the stock to the shotgun!!