[rails] [acts-as-taggable-on] update owner tags via form

Question

I would like to uniquely use owner tags in my app. My problem is that when I create / update a post via a form I only have :tag_list:

<%= f.text_field :tag_list %>

which only updates the tags for the post but has no owner. If I user :all_tags_list

<%= f.text_field :all_tags_list %>

it doesn't know the attribute on create / update. I could add in my controller:

User.find(:first).tag( @post, :with => params[:post][:tag_list], :on => :tags )

but then I have duplicate tags, for post and for the owner tags. How can I just work with owner tags?