Is it possible to whip egg yolks into soft peaks?

Egg yolks can be beaten but they will not achieve the consistency of soft peaks. Beating egg whites on the other hand is generally for meringues or similar dishes - in that case it is vital to separate the eggs carefully because egg yolks contain fat, and any trace of fat, oil etc. will prevent the egg whites from forming peaks when beaten.

http://www.deliaonline.com/how-to-cook/eggs/how-to-whisk-egg-whites.html

Egg yolks (or combined whites and yolks) can be beaten for use in omelettes or similar recipes, but they will have a different consistency.