I found Sonar too fiddly to operate with touchscreen. What would work for me is a fullscreen toolbar with a massive transport and other main functions that do not require touch and drag. Just tap to select basically. And make the buttons massive. Maybe put some jog/scrub forward and backward buttons on there too.

This was sent as feature request before : With multi monitors as common DAW setup, toolbar windows can be opened more than once, for example, one toolbar at the far left and the other at far right. Alternately, tool bar should be able to be expanded more than one row (items on the far right that is not visible drop down to a new row).

What if one can strap a small touch ipod like device (Bluetooth or wifi) on the dark side of the forearm which can include the tool bar. 
 
Perhaps a watch or a smaller device that fits on the index finger with three or four buttons and operated by the thumb.
 
How about a double tap of thee fingers to bring up a large transport.