I'm not aware of any automated tools for the conversion. You might try to search for some using Google, but there will be several caveats along the way. The problem isn't only that the syntax is different. Some PL/SQL construct might not be possible in MySQL at all (eg. analytic functions in SQL statements, if they were used). Something might simply be done differently in Oracle than in MySQL (Oracle, for example, has global temporary tables, while MySQL would create a temporary table on the fly). But the worst is that some things might be easily ported, would be working at the first sight, but might be severely broken after the conversion: Oracle uses multiversioning concurrency control, while MySQL uses locking. Procedures that are valid for multiuser environments in Oracle might not work in MySQL (they might produce deadlocks, or -even worse- plain wrong results).
In short, the conversion will be anything but easy. You'll probably need someone who is very well versed in MySQL and at least comfortable with PL/SQL, to make sure he'll get the transition right.