Hmmm… my first thought is making your own marshmallow for your RKT. If you’ve never made it, it is fairly easy and tastes great. You would just need to find a vegan substitute for the gelatin. I know there are vegan substitutions for gelatin like agar-agar, but you would need to play with the recipe to get the right consistency. As for the margarine/butter in the RKT, just leave it out. I always leave it out when I’m making RKT for sculpting – they don’t taste AS good, but they hold up better to carving!