I was able to reproduce the issue in a local test and unfortunately the rotation cannot be relative to the left end of the label. I would suggest trying to provide more space for the chart or format the values for the X-Axis.
For example you can cut the long strings or put new lines in them. If you populate digits you can use DefaultLabelFormat. More information about label format and examples can be found here:
I hope this helps.
the Telerik team
Let us know about your Windows Phone 7 application built with RadControls and we will help you promote it. Learn more>>