Oh my! If the leak is bad enough to create "diesel steam" I don't think I'd drive it until the return lines are fixed.
I highly recommend you get the "official" hose, either from Performance Products, here on FastLane, or your Mercedes dealer. It is cheap compared to starting a fire from a leak.
It is some kind of metric hose, it just pushes onto the injector fittings and is not a high pressure issue - it just returns fuel. The proper hose is fiber reinforced on the outside.
Please. Save yourself a lot of trouble. The proper hose might cost you $8 or $9 at most.