Unfortunately you would not be able to achieve the desired functionality as the current version of WinRT framework does not support it -- the WriteableBitmap.Render(...) method is missing so you cannot render any XAML control with a bitmap right now (a prerequisite for export to image).
Also, the current version of the control does not support export to Excel functionality either.
Let me know if I can assist you in some other way.
All the best,
Ivaylo Gergov
the Telerik team
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