Multiple selection in FPM form GUIBB

Hi All

I have developed a FPM  application using FPM Form GUIBB, for one of the fields the requirement is user can select muliple values from the selection.In FormGUIBB I can't see any possibility to do this. Any idea how that would be possible, using List GUIBB, I can see the possiblity, but how for one field with in the form, I can do this ? any idea how this can be sorted out.

regards

Anup