Swap for Cake Margarine in the U.S.? A Great British Bake Off question!

I'm interested in making a show-stopper cake (recipe) and it calls for "Cake Margarine" which is not available in the U.S. What is the equivalent that I can swap for it?

Thanks in advance!
My understanding is that "cake margarine" is regular margarine which has been whipped to incorporate air. As long as you're using a stand mixer to cream the margarine and sugar (and do so at high speed), I suspect regular margarine should be fine, as that creaming step is intended to accomplish the same thing. If you chill the mixer bowl in the fridge, it'll help avoid overheating the margarine during creaming, giving you more leeway for a longer beating time.