I usually create postage label through My Post and then send the buyer the label as an image through eBay messages, upload to the request, or send the PDF directly to their email address. I'm not sure if there's an official way through eBay, though sometimes the buyer gets the option to generate the label through their account and it get's charged to the seller's account. 

You may be able to go to the original order and create a postage label from there, it will pre-load the buyer's details, but you should be able to edit it to your own, however this will upload the tracking number to the buyer's order. Currently you'd not able to create postage labels on eBay except through an order, though there was talk of that becoming available at some point this year.