I would like the ability to specify the activation method for the Pan Drag command (by default with Middle Mouse button).

At least two options that would be available would be:

Click and Hold - If the user clicks the Middle Mouse button and holds it, then they can pan drag across the view. As soon as the Middle Mouse button is released, the Pan Drag command is deactivated and the interface focus goes back to how it was before the command was initiated

Singe Click - If the user issues a click, then the Pan Drag command is activated. Releasing the click keeps the Pan Drag command activated. Another click and release would be needed to deactivate the Pan Drag command

Currently, there are some methods to implement this functionality, but it is indirectly controlled. For example, set the Click Sensitivity to Pen and enable drag operations within User Preferences>Input category.

This would achieve the desired results, but the functionality is indirectly controlled here. User requests a direct control of this functionality.