Formatted text through data template?

Hi,

I would like to create a data template which renders a string containing
some known patterns in a specific manner (e.g. subscript/superscript). Think
of a template which renders mathematical formulas which are passed in some
formal language. Given the rich text support in WPF this should not be too
hard.

I tried to achieve something using TextFlow and a custom converter in Jan
CTP but this is no longer available (and I was out of luck anyway since I
could not get my converter being called).

Could someone provide some guidance how something like that could be
achieved?

Thanks
Uwe