All I can say is AMAZING !!! Your home renovation and dream tank are both amazing.
Like you, I also run a closed loop and I didn't want to see all the returns pointing forward. The solution turned out to be very simple and is what is used in the big display tanks at Disney Orlando. It's called Polygem 307 lite and I used it to disguise the returns as little cave openings coming out of the rock work. It worked perfectly! It's also by far the best product to epoxy rocks together so you can easily create 'rule of thirds' aquascapes with shapes that inspire and stay secure. It's very strong and natural looking, like live rock, if you don't use any coloring additives. Rub a little sand over the epoxy while it cures and it will blend in with your rock work and add to your already amazing system (and home). You won't regret having this epoxy on hand.
Polygem #307 Lite - 2 Gallon Kit - Sculpting Epoxy Putty
_http://www.polygem.com/products/zoopoxy/sculpting/307-lite-2-gallon-kit-sculpting-epoxy-putty