Need to use a stored function in a prepared statement -- HOW?

[Don Ireland]

I'm trying to set up a prepared statement. But one of the fields needs set by a stored function. When I try the following, I get an error message "Fatal error: Call to a member function bind_param() on a non-object in ......".

$stmt = $conn->prepare("INSERT INTO `transactions` (`payee`,`date`,`memo`,`acctID`,`ref`,`hasChildren`,`userID` ,`rBalN` ) VALUES (?,?,?,?,?,?,?,getRunningBal($uID,$txn['acctID'],$txn['date']);");


How can I go about using the stored function to set the RBalN field?

Don