One method of 'locking out' overdrive when moving has been mentioned at various times by both Kaiser and Studebaker folk, about what to do in a suddenly hilly scenario. I give no guarantee that you will not wreck your transmission, and I have never done it myself, but for what it is worth.....
In overdrive (assume in third gear) shove the gas pedal down hard and hold it down tight to engage the kickdown mechanism and hold it in direct, and while it is in 3rd direct instead of overdrive, pull the lever all the way out of lock the transmission in direct and keep overdrive from re-engaging when you let up on the gas pedal.