How to increase memory limit for PHP over 2GB?

Have you tried using the value in MB ?

php_value memory_limit 2048M

Also try editing this value in php.ini not Apache.

I would suggest you are looking at the problem in the wrong light. The questtion should be 'what am i doing that needs 2G memory inside a apache process with Php via apache module and is this tool set best suited for the job?'

Yes you can strap a rocket onto a ford pinto, but it's probably not the right solution.

Regardless, I'll provide the rocket if you really need it... you can add to the top of the script.

ini_set('memory_limit','2048M');

This will set it for just the script. You will still need to tell apache to allow that much for a php script (I think).