Couple of suggestions for stretching slippery skin:
1) Use a small cloth or paper towel wrapped around fingers to stretch the skin
2) Wet your thumb or first and second finger tips and then wipe off the skin about to be stretched. Rinse the lather/ oil off of the fingers then try stretching the skin. The area to be shaved may loose some lather this way, but the whiskers will still be moist, and this should not impede the shave at all.
