I think we can work out something. Do you mean previously selected as in previous games or in the same run when you enter the same scene? The basic idea would be to keep the choices in a user variable (RenJS.logicManager.vars) so that they are saved along the story progress. Then the GUI would have to read this list and greying out the options (could be with a different sprite or by adding a tint to the button). If you want to keep the greyed out options between different runs, it would have to be saved in a different way, but it shouldn't be so hard.
Let me know what are your specific needs and I'll help you implement it.
Cheers!