Dear dralban,
From what little I know about long putters, there are three things I would advise:
1. Regardless of whether you use the shoulders or the hands to move the putter, always return the putter sole to the same space it occupies at address before impact.
2. The putter head should not be positioned far from the feet -- whatever gets the bottom flat is as far out from the feet as you should go with the putter head -- this helps reduce the tendency of the putter head to fall in towards the feet during the downstroke.
3. The rear hand (right for a right-handed golfer) needs to "support" the shaft so that the putter during the down-stroke does not drift inward towards the feet.
I could elaborate a little on these three points, but the gist is that the motion back and thru needs to be fluid, does not collapse in towards the feet coming into impact, is managed by a stable pivot (handle held to chest and chest held stationary and / or shoulder frame moves about an unmoving center), and the putter face and putter head return exactly to the starting address position in space just before impact.
The precision of the stroke, as with the conventional putter, depends on the putter face moving straight and squarely thru the center of the ball online to the target, and this usually means that the pivot at the top of the putter or base of the neck stays still in space (even if rotating in place) as the putter head naturally and slightly rises into the back of the ball and thru impact.
That's about all I can suggest for the long putter. I suspect that the problem many have with distance control with the long putter on long putts would be reduced is the stroke is made more with the shoulders than solely with the hands.
The book
The Long View of Improved Putting is the only book I've seen that deals strictly with the long putter.
Cheers!
Geoff Mangum
PuttingZone.com
http://puttingzone.com
Golf's most advanced and comprehensive putting instruction.