<ctrls:ModalPresenterControl ModalToShow="{Binding ActiveModal}">
    <ctrls:ModalPresenterControl.ViewToShow>
        <Grid>
            <ContentPresenter Content="{Binding ActiveView, Mode=OneWay}"/>
        </Grid>
    </ctrls:ModalPresenterControl.ViewToShow>
</ctrls:ModalPresenterControl>