for bobbins, you can do what some of the Nationals do. They have a coil spring "cord" that goes around the belt groove to the bobbin winder, and you only put it on for that use.
http://www.quiltingboard.com/vintage...t231774-2.html
This thread has some pictures of it - for the singer, you'd use the belt groove on the flywheel, but hopefully this will give you a general idea what I'm referring to.