Pre Populate from CSV

Do you guys know how to prepopulate a dropdown from a csv file on the server?

I would do it through the admin area, but the file is 30,000+ lines so that admin interface freezes when I try to save the form.

This is what I attempted with, but no luck

add_filter('gform_pre_render_7', 'GF_prepopulate_2');
function GF_prepopulate_2($form){
		 foreach($form["fields"] as &$field){
            if($field["id"] == 15){
					$csv = array();
					$file = fopen('http://example.com/mf.csv', 'r');

					while (($result = fgetcsv($file)) !== false)
					{
						$csv[] = $result;
					}
					fclose($file);

					foreach ($csv as $line){
								$field['choices'][] = array( 'text' => $line, 'value' => $line);
							}
				}
			}
	 return $form;
	}