What is a substitute for half-and-half cream?
When I am substituting in a recipe, I usually use coconut cream instead of cream or half and half if called for in a recipe. (There is a question posted here that covers how to get the cream from a can of coconut milk.) Sometimes I use soy creamer, but sometimes that can be hard to find. I'm sure you could experiment with a mix of soy creamer and soy milk.

My ideal solution is to use vegan recipes to start with, because they are formulated without milk or eggs. Maybe in your case, just look up dairy free cake recipes, if you don't mind eating eggs. There are a lot of cookbooks and blogs out there with a ton of vegan cake and dessert recipes.