Not sure what kind of a drive you'd have to the nearest mechanic/garage, but if this is getting out of hand, you could pinch off the line with vise grips (pinch and fold over and pinch again) and limp over with front brakes only. Just before doing this, fill the resevoir and pump the pedal to fill the rear line. I'd only suggest this as a last resort, of course.

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1986 560SL
2002 Toyota Camry
1993 Lexus