That's a good idea, but not currently supported. Roles can be assigned for a specific duration. If you you are able to troll through the code for usage examples (those invoked by the RS bulk admin forms), it would be possible to write your own code to automate duration-limited role assignments via calls to ScoperRoleAssigner::assign_roles() :

function assign_roles($scope, $src_or_tx_name, $item_id, $roles, $role_basis = ROLE_BASIS_USER, $args = array() ) {

    $defaults = array( 'implicit_removal' => false, 'is_auto_insertion' => false, 'force_flush' => false, 
'set_role_duration' => ", 'set_content_date_limits' => " );

…but I don't have time to further document or consult on that right now.

Current functionality supports manual assignment of a role with explicit start and/or end date specification. You're asking for automatic assignment (upon registration) of a role with dynamically generated end date of "now + 30 days".