I'm afraid that you can do that only by code.
You will have to modify the category_item.php in order to fetch specific extra fields.
First of all you have to create K2 overrides, if not already. Read here (
getk2.org/documentation/tutorials/174-templating-with-k2-and-the-concepts-of-sub-templates) how the overrides work
Then open category_item.php since this is the one you want to show the specific extra fields.
Locate the extra fields block of code and use this code snippet to fetch each extra field
<?php if ($this->item->extraFields->Your_extrafields_alias):
echo $this->item->extraFields->Your_extrafields_alias->name;
echo $this->item->extraFields->Your_extrafields_alias->value;
endif; ?>
