0.72 to 0.9 can be achieve with a 1.25X viewfinder magnifier
0.72 to 1.0 can be achieve with a 1.40X viewfinder magnifier
http://en.leica-camera.com/photography/m_system/accessories/viewfinder_accessories/2211.html
Just plug and play.
To go wider, it's best to get an external viewfinder. Much cheaper anyway.
To physically convert the viewfinder, not many can do as parts have to be ordered. Schimdt can probably send it in to Leica Germany for you if you can spare the time and money.
Cheers,