How can I add an additional colormap option to a GUI colorbar?

Hi,

I have a GUI with a figure. The figure makes a contour plot and has a colorbar. When the GUI is running there is a (standard Matlab) feature where you can right-click on the colorbar and a menu appears. One of the options is 'standard colormaps'. I would also like to include a feature whereby I can load a range of different custom colormaps here. Is this possible to do or does anyone have any suggestions for how this might be done?

Thanks for any help in advance.