Just found an pretty straightforward solution for this problem:
add_action( 'template_include', 'account_page_template' );
function account_page_template( $template ) {
if( isset( $_GET[ 'account' ] ) ) {
return locate_template( array( 'account.php' ) );
}
return $template;
}
But as it seems only natural to use some kind of permalink stucture for these kind of things here is a part of my final code that make urls structures like example.com/account/user_name possible:
// Register to query vars
add_filter( 'query_vars', 'add_query_vars');
function add_query_vars( $vars ) {
$vars[] = 'account';
return $vars;
}
// Add rewrite endpoint
add_action( 'init', 'account_page_endpoint' );
function account_page_endpoint() {
add_rewrite_endpoint( 'account', EP_ROOT );
}
// Load template
add_action( 'template_include', 'account_page_template' );
function account_page_template( $template ) {
if( get_query_var( 'account', false ) !== false ) {
return locate_template( array( 'account.php' ) );
}
return $template;
}
In the acccount.php template you can fetch the parameter value like this:
$user_name = get_query_var( 'account', false );