How about just a natural low EEb (no valves) TUBE for the opening of "Das Rheingold." With about 14 feet of tubing, the bell end could be engineered to come up right next to the 8th horn player and even face to the rear. I forget and am Too lazy to count, but something like 70 some bars of EEb, while all those sexy German water sprites (sorry Rheinmaidens) "schwim" in "der wasser" singing German words that all begin with "W." 
Then the D flat tuba could be picked up for some of the following episodes. 
Paul (who likes to quote Mark Twain on Wagner: "I hear it on good authority that Wagner's music is really much better than it sounds.") Maybery.
PS. "Der Ritt" works nice on a FIVE valve CC. Just saying. 5 VALVES. Thought it did take me 40 years to get it.