My boyfriend wants a pumpkin cake... how can I add to this recipe?

I found something on Pinterest that tells me to mix a can of pumpkin with a box of cake mix, and it eliminates the need for eggs and oil. Okay, fine… but it won’t have the delicious pumpkin flavor if it’s just canned pumpkin. I can’t use the pie filling because it’ll be super sweet since it has added sugar. How much pumpkin pie spice do you think I should add? I don’t want to under or over spice it.