Thank you very much for responding so quickly with that.
I changed all of the 'php_admin_value' directives to just 'php_value' in that file but I was still unable to change the 'session.save_path'.
A little more digging and I found that the 'php_admin_value' directives are ALSO in the vhost files for each site and must be overridden there too.
The only downside is that unless I modify the vhost template, then the next time I save this site the vhost file will be re-written and I'll have to make these changes again. That is a small price to pay, because without being able to override 'session.save_path' my entire site goes down.
Feature Request Please Falko?