Either or option for layer list or legend widgets

Hi - I was wondering if anyone has modified the layer list or legend widgets so that only one operational layer can be turned on at a time - i.e. when the viewer ticks one layer on any previously ticked layer is unticked.

I have not yet got started on flex development, installation of the api etc - I am kind of hoping it may not be necessary if this option is already available!

Kind regards,
Ben