Filter Gravity Forms checkboxes based on user_meta value

gistfile1.php

<?php

add_filter( "gform_field_content", "mz_disable_completed_series", 10, 5 );
function mz_disable_completed_series( $content, $field, $value, $lead_id, $form_id ) {


  //only manipulating checkboxes for form id 1
	if ( $form_id != 1 )
		return $form;
  
  // only interested in field id 1
	if ( $field['id'] != 1 )
		return $form;

	// get current user (users must be logged in to view the page/form)
	$user = wp_get_current_user();

	// Get our items that we need to disable
  // returns an array of id's that match checkbox values
	$completed_series = get_user_meta( $user->ID, '_completed_series', true );

	/*
		prints:
		Focus = 7
		Motivation = 5
	*/
	foreach ( $completed_series as $c ) {
		$term = get_term_by( 'id', $c, 'performance_factor' );
		echo $term->name . " = " . $term->term_id . "<br>";
	}

  // These checks were taken from the developer docs
  // Not sure that we need them
	if ( rgar( $field, "type" ) == "checkbox" ) {
		if ( RG_CURRENT_VIEW == "entry" ) {
		}
		else {
      
      // loop over field choices
			foreach ( $field['choices'] as $c ) {
        
        // we only want to match field choices whose value is in our user_meta array
				if ( in_array( $c['value'], $completed_series) ) {
					echo "MATCH: " . $c['value'] . " " . $c['text'] . "<br>";
					// MATCH: 7 Focus
					// MATCH: 5 Motivation
          
          // WHAT DO I DO NOW? How do I either:
          // 1. Add the disabled attribute to the field
          // 2. Add a class or some trigger so I can disable via js
          // 3. Remove the field, though this is far less ideal
				}
			}
			
		}

	}
	return $content;
}