I put parchment on the bottom of the pan (cut to size for my 9" cake pan) and cut a strip to fit around the edge, so all surfaces were covered. I let the cake cool for about 10 mins before turning it out.Your idea came thru 16 minutes before I read it.
I am going to make such a cake. Yes,, The oranges will be peeled, since the poster mentioned the bitterness.
Now I still have a question.
I never made an Upside-down cake. How do you remove from baking pan without it falling apart???
I was considering lining pan with parchment. I mainly use steel pans. Used Pyrex bowls,,, but only when I bake Flan.
Silicone pans are nothing I want to consider.
Good luck with your cake.
Are you following a recipe or just kind of winging it like I did? I think without the bitterness, this could be a really good, easy recipe. I would definitely recommend the melted butter/brown sugar poured over the orange slices before you put the cake batter in. It gave it a delicious caramel coating on top. 

