Hi vinasiam,
The latest Test Versions V4.34i (see the wiki) support 8 Axes GCode XYZABCUV under KMotionCNC. Although there aren't Jog Buttons added for the UV axes, but GCode, MDI and so forth should allow you to control them.
Another option if you don't need to move all 8 axes at the same time is to on-the-fly reconfigure which 6 axes are in use.
Regards