Rans Enduro Sport, Hase Kettweisel Tandem, Merin Bear Valley beater bike
There's always a way but it depends on the particular derailleur and bike. One way is to run cable housing all the way from the shifter to the derailleur and tie it to the frame tubes with wire ties. Like filtersweep said: "It might not be pretty."
'71 Gitane Super Corsa, '73 Atala Giro d'Italia, '73 Schwinn Super Sport, '76 Viscount Aerospace Pro, '81 Miyata 710, '81 Lotus Classique, '84 Ross Signature 290s, '84 Shogun 500, '85 Miele Gara, '87 Miyata 512, '89 Centurion Ironman, many more
I have a dept. store Huffy 12 speed out in the barn with all the cable guides and stops front and rear cast into the derailler mounting, which champs onto the seat tube and rear dropout. Never saw anything like it before....