Thanks for the info James. I guess the only option for now is to give them access to Google Analytics.
In case someone else has the same problem…
It turns out I didn’t read the instructions very well. This was an action and not a filter…
add_action( ‘fue_before_variable_replacements’, ‘fuekb_register_variable_replacements’, 10, 4);
function fuekb_register_variable_replacements( $var, $email_data, $fue_email, $queue_item ) {
$variables[‘testvar’] = ‘test value’;
$var->register( $variables );
}