What I've done in similar cases is use a flaring tool to lightly flare the tubing. You can then slip the 3/8" rubber fuel line over and past the flared area and then clamp with 2 hose clamps. The flare acts kind of like a "safety stop" - there's no way that the fuel line can slip off. Don't clamp ON the flared end, clamp about 1/4" away from it.