I've been using the door stops for years...2-3 under the back of my machines. Don't do this when machine is in embroidery mode (if you have an embroidery machine)...It will throw the calibration off. I also have a quilting extension for my embroidery machine and can use a couple under the legs of it as well. I don't use the "tilt" on my serger either. Don't think it would be good for the machine...plus the fact, it's not really needed for that one.
Hugs, Drue