Implementing non-zero length, freely pivoting springs

[drussel]

I'm looking for the best way to implement a freely pivoting spring with non-zero length between two rigid bodies. That is, I want to restrain the distance between a point of each rigid body and otherwise not constrain the orientations of the rigid bodies. If the bodies are spheres, the anchor points are the centers, and I only have one such spring, I can get away with using the, eg, x coordinate of a btGeneric6DofSpringConstraint to provide the length. But this approach doesn't work for more complex bodies or for more than one spring involved in each particle. So I could add extra rigid bodies with very small mass to defined the attachment points and use the spring constraint on those. Is there a better way? Thanks very much.
--Daniel