Update Binding Source on Unfocused

Hi,
Does anyone have a suggestion on how to, for example, only update the source property of an Entry's Text binding when Unfocused rather than TextChanged? XF doesn't seem to have the ability to specify UpdateSourceTrigger like in WPF. This is problematic when you have calculations and visual drawings based on the property. Every keystroke sets off recalculate and redraw.

Thanks,

Chase