Is there a way to remotely authorize any MAC address or name with a voucher code? 

I've had scenario were I'm not available then someone wanted to purchase a voucher, but I rather grant them access to the network with a voucher than sending the code to them(for fear or shearing) or just authorizing them by clicking in the clients list tab? 

I've authorize a few connections via the clients tab then forgot to unauthorize them after their time expired.