Add product specific fee, not cart-wide fee

I need to give flat fees to specific products so that they show up on the line item totals. It appears that I can do this through use of a hook (woocommerce_before_calculate_totals or woocommerce_after_calculate_totals) and by altering the cart items in the WC_Cart object. However after I do this, any changes I make to line_subtotal and line_total are wiped away by the time everything is spit out to the cart.

Is there a way to do this? Here is the code I’m using:

 add_action( 'woocommerce_before_calculate_totals', 'calculate_product_totals_with_hidden_tm_epo_fees' );
 function calculate_product_totals_with_hidden_tm_epo_fees( $cart_object ){
 
 
    $cart_contents = $cart_object->get_cart_contents();
 
    foreach ( $cart_contents as $cart_content ) {
 
       if (sizeof($cart_content['tmcartfee']) > 0){
 
          $cart_content['tmcartfee_hidden'] = $cart_content['tmcartfee'];
          $cart_content['tmcartfee'] = array();
          $cart_content['tmdata']['tmcartfee_data'] = array();
 
          //Fees are hidden and overridden. Now you calculate everything in:
          // 'woocommerce_before_calculate_totals'
 
          foreach ( $cart_content['tmcartfee_hidden'] as $fee ) {
             $cart_content['line_subtotal'] += $fee['price'];
             $cart_content['line_total'] += $fee['price'];
          }
       }
    }
 
    $cart_object->set_cart_contents($cart_contents);
 
 
 }