Currently, while selecting troops for a battle, only those available are displayed. You can close the window, go back to the city, select the barracks, and grab that one keen item or hero off of your healing HI. Then you exit the barracks, go back to the main map, select the hex, and equip the item for the battle.
If troops unavailable due to healing were displayed but greyed out/not selectable in the battle selection screen to the right of the usable units, it would add a nice level of functionality to the GUI.
Thanks.