I’d like to display (e.g. in a TextBlock) the fractional part of a float using a smaller font size like this:

The float value comes from a binding, so it’s not static text.
I’m currently using two Run objects with different font sizes inside a TextBlock — each of which have a binding to the same float value with converters that return the integral, and the fractional part, respectively. But I don’t like that this involves two bindings.
Is there a better way to achieve the same result?
one idea of improvement : only one converter, and a converter parameter to get either integral or fractional part. (or no parameter for integral, and ‘frac’ for fractional).