I think you can use 'gearman' to spawn a job from PHP and receive a serialized result from PHP. After this you can use PHP::Serialization(CPAN) to deserialize or JSON to bring the results with Perl(JSON probably is more simple). Gearman site:

• Gearman official site
• PHP and Gearman

Off course you will need to install Gearman in A and B servers. If you canīt do this, you can use simple sockets to get results from PHP and finally process with Perl anyway.