Unfortunately I don't think this is possible.
A number of years ago we wanted the same functionality for dropdown components etc, but were told by Kentico Support:
As we understand it, you are trying to build some ultimate universal dropdown component, that will accept all data types. In our experience this could be problematic.
Based on this, I would recommend that you parse the value within the widget's viewcomponent to get the correct integer value (possible using ValidationHelper.GetInteger
).