I use a lot of scrub (J) in the Piano Roll View.
But the inconvenience is that Scrub modifies the Now Time leaving it equal to the position where I released the left mouse button.
Is there any way to preserve Now Time in its original position by using Scrub?

I highly doubt it. You're manually moving the now time, not initiating playback with the transport. When you initiate playback, SONAR knows where your now time started. If you move the now time, SONAR accepts that as a new now time.
 
I guess there would need to be some mode where if you had the J key held down, SONAR would think you were using the transport for playback, and would therefore remember where the cursor was when you started moving it.