No need to cut subjects
Consult a road range of scientists, techologists,engineers etc, get them to look at the cuurent curriculum to see how to incorporate stem items into existing classes.
A simple example might be, in art classes introduce the tools for art, why do we use a brush? How does a brush work? With capillary action and the flexing of the bristles...
In reading comprehension use passages that include stem content at the relevant level.
As a ten year old I had a teacher who was an ex armourer on WWII aircraft, he taught us how and why a machine gun works, that brings me to the key to teaching anything, make it interesting to the audience you have.