Filter Custom fields from categories

Hello,

I have a menu that is setup with a Category listing called "authors".
I have created a Custom Field into the Categories table called Group.

When i try to create a Filter to appear in the "authors" menu, I select the type and then i select to apply into a custom field. But when i try to select the Custom Field ""Group" that i've created into the Category Table it doesn't appear in the list.
It only show the Products Custom Fields.

Is it possible to use Categories Custom fields within the Filter?

Unfortunately i'm not a developer yet...
Do you think that a next version of Hikashop will be prepared to use the filters with category listing?

For now the only way i see to workaround this is to create my authors as a product and then create a product relationship. This way i can enter the author and see what product he's responsible to...

Thanks

By the way,,,, i created an alphabetical custom field and a filter for it but it appears vertical on the site. How can i setup horizontal??