Scroll horizontally the branch explorer using Shift+Mouse-Wheel or Ctrl+Mouse-Wheel?

[mdel]

In the "classic" version of PlasticSCM GUI mouse scroll were scrolling the branch explorer horizontally.

In Plastic X the mouse scroll vertically. This is a good improvement.

I wish to still be able to scroll horizontally, but I did not find how to do so. I am expecting Ctrl+Mouse-Wheel or Shift+Mouse-Wheel but those does not make it scroll horizontally