Automatic order status linked to payment method magento

Hello, We want the following done: When a customer has paid with one specific payment method (payment afterwards / downpayment) the status after invoice & send should not be status "complete" but a custom status named "rest payment asked". This process has to be automatic. Please pay attention! It's not the status name after ordering, It's the status name when the item is completed (invoiced & send). Can someone make this for us? Thank you for your answer.