Code to Write to Wp-config.php

I would like to be write some code to add a line to my wp-config.php file automatically.

Background:
I have about 100 sites that have no revision limitations on them. I would like to use ManageWP to just send over a code to add the following to my wp-config.php file (kind of like Super cache does when it is activated).

/*Optimization Stuff */
define('AUTOSAVE_INTERVAL', 120 );  // seconds (default is 60)
define('WP_POST_REVISIONS', 5); // alter number of post revisions kept.

Does anyone know the php that would insert this code into the wp-config.php file? Thanks for any thoughts you have.