The radalt works perfectly in the context of my post, Walter. Such procedures are carried out hundreds of times every day in all kinds of weather around the world. The baro alt, with no exceptions that I know of, is set to QNH. I accept a radalt won't stop you flying into a cliff if you're intent on doing so.
Other than that I can't follow your logic. Sure, a QFE could be used as you describe. But so could a QNH without the requirement of being the same level. And this would also give your level relative to any spot ht (or cliff top!) on your chart.