Simple Doesn't use Special Delivery but automatically covers sellers up to £750 for loss or damage in transit.
If you really want to use you could have "free postage - seller pays" on your listing and factor that cost into your item price. Then buy your own postage. You have to open the ebay label to get buyer's address and mark dispatched. You can't change the tracking now but send in message to buyer. You would still be able to add the new number to a "not received" case if one was opened. You can then cancel the ebay label to get a refund of that cost.