Hi,
if i understood well you may want to do a custom field type
http://www.advancedcustomfields.com/resources/tutorials/creating-a-new-field-type/
to check if this is what you want have a look at the following tutorial
http://vimeo.com/33099101
that will give you grate control over how you field is displayed.
but it’s maybe too heavy for what you are trying to do.
