I found this on Fat-Free Vegan, and by golly it works. I made up a batch and now I won't ever have to buy the stuff again. The main reason I decided to make it was because the commercial egg replacer contains citric acid, a no-no for one of the people that will be eating the wedding cake. This homemade version is citric acid free. Bonus: now I have some fancy flours for trying out some gluten-free recipes (I think my friend Ally might enjoy them).
Homemade Egg Replacer:
1 c. potato flour
3/4 c. tapioca flour (or starch, same thing)
2 tsp. baking powder
Combine all ingredients and mix until well-combined. Store in an airtight container.
1 1/2 tsp of mix + 1 Tbsp water = 1 egg yolk
1 1/2 tsp of mix + 2 Tbsp water = 1 whole egg
I usually mix it up first, then add it to the batter, though I know some people don't. The original recipe suggests that you shake it up in a screwtop jar first, but I found that whisking it up in a small bowl worked just as well.