Dynamically populate drop down with user info

All of the tutorials I am seeing for dynamically populating a drop down aim to replace the drop down options with a set of data (like adding certain posts to the drop down). What I am trying to do is dynamically choose an option from the drop down based on previously entered user information.

For instance, I have set up a custom user field for country. When the user registers, they choose the country they are in from a drop down. I am trying to have my gravity forms automatically choose the country that they selected upon registration, but leave the defined drop down options available. I have been able to dynamically populate text fields with custom user information with a function like this:

// populate the field with "user_title" as the population parameter with the "user_title" of the current user
function env_populate_title() {
	$s2title = get_user_field ("title");
	if ($s2title == '') { $value = populate_usermeta('user_title'); }
	else { $value = $s2title; }
	return $value;
}
add_filter('gform_field_value_user_title', 'env_populate_title' );

I know I need to pre-render the form to apply the drop down value but I'm not sure how to just select the value and not replace the drop down choices. I know that this is not there yet but it should be something similar to this:

function env_populate_country($form) {
	foreach($form['fields'] as &$field):
		if($field['type'] != 'select' || strpos($field['cssClass'], 'country') === false):
			continue;
		else:
			$choices = get_user_field ("country");
			$field['choices'] = $choices;
		endif;
	endforeach;
	return $form;
}
add_filter('gform_pre_render', 'env_populate_country');

Please help...

This needs to apply to all forms, none of which are multiple page forms.
Any chance there is someone that can help me with the jquery option? Without knowing more, I don't really know what you mean by hooking to the on change action. Exactly what is changing within the jquery realm that would open the possibility to hook to it? Where/when is the on change action happening? I can't even begin to guess at how that would work.

For the benefit of other user who might be trying to accomplish the same thing, this function does work to pre-select the country dropdown.

/* populate the field with "user_country" as the population parameter with the "user_country" of the current user*/
function env_populate_country() {
	$s2country = get_user_field ("country");
	if ($s2country == '') { $value = populate_usermeta('user_country'); }
	else { $value = $s2country; }
	return $value;
}
add_filter('gform_field_value_user_country', 'env_populate_country' );

I wasn't seeing it at first, but I logged out of my user and logged back in and it kicked in. Also, just some advice separate from this problem, make sure that the values and labels match between the user registration drop down (or where ever you collect the data) and the drop down that you are trying to populate. For countries especially, I've found that those values can vary.