A single quickslot which when you mouse over it, and scroll with your mouse wheel, you scroll through all your mounts.
In the manager screen for the Carousel of Horses you can drag and drop all the mounts you have which you'd like to be on your Carousel. Or all mounts you have could be detected when you get this plugin, and you uncheck a box next to any that you don't want in your Carousel.
You can place this quickslot anywhere you like using Ctrl\
An example of an existing plugin with a single quickslot in which you can use the mouse wheel to scroll through musltiple options, is found in the KragenBars tactical buff quickslot for Captains.
http://www.lotrointerface.com/downlo...ragenBars.html