That won't work, either, if the cashier is strict (any many are). They'll ask to see I.D. and if you can't produce it, they won't proceed with the transaction. I've run into some cashiers like that in the past, when I was using someone else's card. Then they'll try to take the card away on top of it. So what you suggest might or might not work, depending on the cashier's mood that day. And some are real jerks about it.
I've never loaned out my card, but the person I split my card with loans her's out to her sisters all the time. She says it works because she is older and her sisters are also older and both somewhat resemble the low quality black and white photo on the card. I assume there's some truth to that since the only times I've ever been ID'd (I look relatively young) is when I wasn't wearing my glasses (that I have on in the photo).
Of course I wouldn't bank on that.