crmEntityRef Populated with Custom Fields from a Custom Group

Question

I would like to use crmEntityRef to load all the fields from a custom group I have created. I would like to have the list show the label for the field, and when selected it would return the id.

The following is what I currently have, but doesn't seem to work.

 $('[name=link_field]').crmEntityRef({
      api: {
          params: {
              custom_group_id: 'Assimilations'
          }
      },
    });

Obviously I'm doing something wrong. Any ideas?

Thanks!