on-the-fly changes to php.ini values?

Hello! I'm working on an Apache2 module which pulls vhost info from LDAP, and I've got it all knocked out save one really important feature: I need to be able to change the open_basedir on a per-vhost basis, but obviously, NOT via php_admin_value in the configuration file(s), since each vhost is loaded dynamically from LDAP data. I dug around a bit and found the zend_alter_ini_entry function, the prototype of which, at least, looked really promising. However, it always returns FAILURE for me. I've tried every combination of mod_type. I went and copied the source for zend_alter_ini_entry directly into my module, which let me determine that the call to zend_find_hash() is what's failing. So this leads me to believe zend_alter_ini_entry isn't really what I need to do this. I also poked around in the per-dir configuration handler (sapi/apache2handler/apache_config.c:merge_php_config), but that hasn't shed enough light on the problem for me to just jump in and start hacking away at the php module config data block. So, my question is: is there a programmatic way, via some function call or procedure, to alter PHP's runtime configuration as I describe above? Thanks and further details forthcoming to anyone who can lend a hand. Todd D. Esposito