These are fun books! I've enjoyed cookies and cupcakes made from both of those cookbooks. Once when I was doing a hard core vegan experiment I decided to try to make key lime pie and I used the recipe from Vegan Pie in the Sky. We didn't love it, although I think that had a lot to do with the gelatin substitute I used. I'll be curious to know how you find the recipes in that one!
I've never used agar powder. I am wondering if I made a custard with corn starch if it would work.