A way to shorten the helper arms of the vanishing point assistant tools without moving the vanishing point

Develop Feature Requests
1

I’d like a modifier to move the helper arm end point along the arm without moving the vanishing point

I can lengthen the helper arms without moving the vanishing point by dragging the mid point past the end point. But if I want to shorten them again I need to use the end point (which moves the vanishing point).