i dunno. i would think since they want it whipped to stiff peaks i'd go with making Isa's Rad Whip. at first i thought full fat coconut milk (skimmed & whipped) might work, but perhaps Rad Whip would be best.
Coconut was my initial thought too, but I think for the sake of fluffiness, I'm going to try the rad whip. Plus I know I can freeze that well (something I was concerned about if I wanted to try soyatoo or something). Wish me luck!