Analytics code with return value

Hi,
I've added a function to get a registration code via a php function in the gform_pre_submission_1

function key_generation($form)
{
require_once(ABSPATH.'/getkey.php');
$_POST["input_3"] = $ResDesc;
}
add_action("gform_pre_submission_1", "key_generation");

Now I want to execute this function:
_kmq.push(['alias', 'bob', 'bob@bob.com']);
where bob should be $ResDesc and bob@bob.com should be another input field.

What's the best way to do this? In which event? can I use the confirmation message?
Best
R