I was able to add a custom field in the quote list partial_quote_table.php
$CI = &get_instance();
$custom_fields = array( 'quote' => $this->mdl_custom_fields->get_values_for_fields('mdl_quote_custom', $quote->quote_id),);
echo nl2br($custom_fields['quote']['Projet']); ?>
which works fine until you consult this page from inside the client tab ??
gives Severity: Error
Message: Call to undefined method Custom_Fields::get_values_for_fields()
So maybe the code inside partial_quote_table.php needs to be in another file for all outside scopes ??