Making C++ OOT module and wish to set up a parameter with different choices!

Hello,

I am making a C++ OOT module and wish to have an input parameter "frame_length" with different choices. I would like to provide short, medium and long frames with a value attached to each. Based on the OOT syntax, I can enter "frame_length" as an input argument to the model. Now, how can I set  up the inners of the *.cc file so that when the module is built into a Gnuradio block, I can simply click on 'frame_length' to see the choices and select one?

Thanks for the help.

Regards,

George