How do you shim the frame of a sliding patio door from one side only (from outside)

Question

The previous owner remodeled the kitchen and he put drywall from inside over the sides of the door and then he painted. I just replaced the door and now I have to align it, level it plumb it and square it

In order to do that I have to use shims but I can only insert them from outside while most of the references I checked show the shimming done from both sides

Is there a way to do proper shimming from one side only? (One way to do it is to use shims from outside to measure what you need (thickness) and them remove them and use a table saw to cut strips as per your needs

Any other ideas?

Answer 1

I ended up stacking two shims and inserting them from the accessible side. the secret is to guess the right thickness that the side that is not accessible to you can take. After that you remove the two shims, you trim them and you put them back