For death saves, they're much easier to do on newer Sterns. They don't require much force at all. Certainly not enough to damage the machine. If done correctly you can do them with only a single tilt warning.
The way I do them is when the ball just starts going down the outlane, I quickly shift to the left side of the machine for max leverage. I then pull the machine to the left (imagine flexing the legs toward you and to the left), when the ball hits the left wall I "pop" it to the right and upward.
The key to death saves is you're not "pushing" the machine. You really have to apply a quick, sharp force at the right moment. If you have to slide the machine more than an inch to do it, your timing is a bit off.