OK, I solved it - but thought you might be interested in the issues I encountered along the way, for future support purposes.
#1 - calling a stored proc is not working, basically due to a permissions issue. The hosting package that I am working with does not give me SUPER privilege on the MySQL database, and without this, I apparently cannot specify the DEFINER as being someone other than my "root" admin user (I'll just call him "xxx" for this post). But when I install Joomla it creates a different user - xxx_joom3 in this case. So, my database connection is to the xxx_joom3 database and it is trying to call a stored proc that PHPMyAdmin created as owned by xxx. Have tried askig for help on this one with my hosting company but in the meantime decided to try something else ... see "#2"
#2 - I worked out how to do the same thing from a PHP script using database.query. It all works beautifully except for one little problem. I need the ID of the PERSON record that was just created. When I call $this->_lastInsertId in my PHP script, even though the script is supposed to be submitted after Fabrik has processed the form, it comes back NULL. If I try to run a query to return the value of the MySQL function LAST_INSERT_ID() it returns 0. I finally had to run a query to SELECT the ID of the PERSON record that had just been created by the form submission. This works but it seems odd to me that using $this->_lastInsertId or running "SELECT LAST_INSERT_ID ()" didn't work. Any comments ?