Does anyone know the Create-a-Sim face blend key?

I've just recently started playing again, and in the old days I used to know a key you could use in Create-a-Sim that saved me a lot of time and made interesting faces. What I used to do was pick a face with unusual and strong features, like the elven face for the pointed ears, and there was some key or combo I could hold down and click on one of the other default default faces, let's say the Asian face, and it would blend the face you had chosen slightly toward the second face. I swear I'm not making this up, it worked great. I think it took maybe 5-7 clicks to go from face A to face b, so it was actually pretty easy to make sims with elf ears and interesting ethnicity if you don't need the ears to be super pointy. It saved me a lot of time with sliders and let me do things it was difficult or impossible to do otherwise, even in Body Shop. It also helped create good breeding pairs because of more subtlely blended features than you can get with the sliders.

Problem is, I have forgotten what key or keys I need to hold down, and this trick was always pretty obscure I gather because none of the online tutorials seem to mention it. I don't suppose anyone knows the key/s and whether it still works with Pets? I think I originally got it from a Maxis tutorial on the EA site that is no longer there.