the lens + P6->F + F->M42(10mm) + M42-Helicoid(15~26mm) + M42->E
With this setting you can focus from 0.5m to (a bit beyond?) infinity.
Yes it is front heavy, but the lens' focus is very smooth, no problem.

Helicoid is fully extended in the above photo, all those adapters are
off the shelf items, including a rather rare F->M42 mount converter.
This one > http://www.pbase.com/kkawakami/image/124972053