Use M42->μ4/3 adapter with helicoid, and filed off bayonet nails in order to attach L->M mount
adapter base as you see in this photo. Micro 4/3 mount base has a quite nice just 38mm diameter.
This helicoid extends from 12mm to 18mm, which is better than M42->M42 adapter with helicoid.
(The left over ring in the right side of above photo is pretty convenient exactly 1.0mm thick.)

----------------------------------------- Important Addition ----------------------------------------------

If you do not want to do this process, you can now get Yeenon's M42->L39 11.5mm Helicoid and
L->M adapter, together US$85 or so. It is easier, all you need is to make infinity focus by adding
shim(s) between lens block (P45m_9) and this new helicoid. But you still have to do 1-11 processes.
When you pick this new helicoid which extends 7mm, your lens' MFD becomes shorter than 0.45m.
Also it is hard to find an M42->μ4/3 adapter today, and you get a better finish. Added benefit of
this is that you already have a lens mount stopper in the L->M adapter, I added it to my helicoid.
See Yeenon helicoid > http://www.pbase.com/kkawakami/image/161506829