I just take a small amount of the oil, a drop or two, rub it between my fingers, then start stretching the lip of the pad that stretches over the cup, gradually increasing the amount of force I use until the slack I've created seems about right. It really does make the material more pliable and easier to stretch. Then, wipe off the excess oil and start stretching the pad over the ear-side baffle. 1 set takes ~30 minutes for me to put on (usually I'm watching TV or listening to music), and removing them and putting them back on isn't nearly as difficult after you've conditioned them like this.
Use a very small amount of oil, a little goes a long ways with that stuff.