I'm doing a baptism cake this weekend and wanted to make a filigree royal icing cross as a topper. I wanted to do something that looked light and delicate so I liked the idea of filigree. My question is how will I get it to stand up on the cake? Also, I know it'd be pretty delicate - if this is a bad idea, anyone have other ideas? I was thinking of making a quilled cross but that just sounds like a pain, haha. Thank you!

There are delicate cross molds, but you don't have time.  

I would make a then gum paste cross to serve as your background (base) and filigree with royal icing on top of it. You can make the gum paste a color to compliment your cake, or pearl dust it to make it look richer.   Make sure you put a thin skewer into the gum paste ahead of time.  That will serve to anchor it into the cake.  

You could try white chocolate finely piped onto wax paper, but I wouldn't put it on the cake until it is in it's final resting place.