You can do some simple username and password obscuring, but anyone who reverse engineers the script will get the username and password.

Consider a different approach. Use MySQL's GRANT to give that username INSERT and UPDATE privs on one table, and no privs to anything else (see GRANT and RESTRICT in the MySQL docs). That way, a malicious user can do nothing beyond making spurious updates to that one table. They won't have visibility to do other tinkering.