I'd recommend against that. We did that for our 4 a few years back. It makes for a very uneven seating experience. It somehow makes the seats feel even smaller than they actually are.
Yeah, I'm thinking we will bring blankets or something to try to level out the middle - guess we'll see how well it works/how much it bothers us. I just really like having the seats clearly defined - no room for confusion/disagreement on space.