I have the code below that is displaying a form and when a user begins filling out the "Credit Union*" field it generates a list of suggestion which they can choose from to populate the field. This is extended from the tutorial on this page:
http://www.ssbits.com/tutorials/2011/create-an-ajax-auto-complete-member-search-with-silverstripe-and-jquery/

Everything is working thus far but I want to add some extra functionality. I want to add a hidden field, a city text field and state dropdown field but if the user uses a suggestion from the list I want it to automatically fill out the 3 new fields. Adding the fields is not a problem. I need help populating the fields based on the suggestion selected.

If no suggestion is selected a user enters custom entry for Credit Union then the fields don't automatically populate.

Credit Unions are a dataObject with the related information.

CreditUnion.php

<?php

class CreditUnion extends DataObject {
	static $db = array(
		'Name' => 'Text',
		'CN' => 'Text',
		'City' => 'Text',
		'State' => 'Text'
	);
	
	static $has_one = array(
		'Page' => 'Page'
	);

	function getCMSFields_forPopup() {
		$fields = new FieldSet();
	
		$fields->push (new TextField('Name', 'Name'));
		$fields->push (new TextField('CN', 'CN'));
		$fields->push (new TextField('City', 'City'));
		$fields->push (new TextField('State', 'State'));
		
		return $fields;
	}
}

?>

FormPage.php

<?php
class FormPage extends Page {
	static $db = array('ThankYou' => 'Varchar(255)');
	
	function getCMSFields() {
		$fields = parent::getCMSFields();
		
		$fields->addFieldToTab('Root.Content.Main', new TextareaField('ThankYou', 'Thank You Message'));
				
		return $fields;
	}
}

class MemberSearchPage_Controller extends Page_Controller {
	static $allowed_actions = array(
		'SignUpForm',
		'results',
		'doSignUp'
	);
	
	public function init() {
		parent::init();
		
		//JS
		Requirements::javascript("http://ajax.googleapis.com/ajax/libs/jquery/1.5/jquery.min.js");
		Requirements::javascript("autocomplete/javascript/jquery.autocomplete-min.js");
		Requirements::CustomScript("
		
			jQuery(document).ready(function() {
				var options, a;
				
				jQuery(function(){
				  options = { serviceUrl:'" . $this->Link('results') . "' };
				  a = jQuery('#Form_SignUpForm_credit_union').autocomplete(options);
				});						
				
			})
		
		");
	}
	
	public function SignUpSuccess() {
		return isset($_REQUEST['signupsuccess']) && $_REQUEST['signupsuccess'] == "1";
	}
	
	public function SignUpForm() {
		// Sign Up Form Fields
		$fields = new FieldSet(
			new TextField('first_name','First Name*'),
			new TextField('last_name','Last Name*'),			
			new TextField('credit_union', 'Credit Union*', $this->getSearchQuery()),
			new EmailField('email','E-mail address*')
		);
		
		// On Submit
		$actions = new FieldSet(
			new FormAction('doSignUp', 'Submit')
		);
		
		// Fields to validate
		$validator = new RequiredFields('first_name', 'last_name', 'credit_union', 'email');

		return new Form($this, 'SignUpForm', $fields, $actions, $validator);
	}

	function results() {
		if($credit_union = $this->getSearchQuery()) {
			$credit_union = Convert::raw2xml($credit_union); 
			
			//Search for our query - Pretty basic example here
			$Results = DataObject::get('CreditUnion', 
				"MATCH (Name) AGAINST ('$credit_union') 
				OR Name LIKE '%$credit_union%'"
			);

			//For AutoComplete
			if(Director::is_ajax()) {
				$Members = $Results->map('ID', 'Name');
				
				$Suggestions = "['" . implode("','",$Members) ."']"	;
				
				return $json = "{
					query : '$credit_union',
					suggestions : $Suggestions
	 			}";
			}
		}
	}
	
	function doSignUp($data, $form) {
		// Store in DB
		$submission = new SignUpSubmission();
        $form->saveInto($submission);
        $submission->write();
		
		// Send Email to Admin
		$From = $data['email'];
		$To = 'email@test.com';
		$Subject = 'Subject';
		$email = new Email($From, $To, $Subject);
		$email->setTemplate('Template');
		$email->populateTemplate($data);
		$email->send();
		
		// Send Email to User
		$autoFrom  = 'email@test.com';
		$autoTo = $data['email'];
		$autoSubject = 'Subject';
		$autoEmail = new Email($autoFrom, $autoTo, $autoSubject);
		$autoEmail->setTemplate('Template');
		$autoEmail->send();

		Director::redirect(Director::baseURL(). $this->URLSegment . "/?signupsuccess=1");
	}

	function getSearchQuery() {
		if($this->request)
			return $this->request->getVar("query");
	}
}