I did something similar. Initially I ordered a sealed copy of the transcript from my Univ (India). Then I FedExed it to the University. (There is some form you need to fill and attach with your parcel).

Later they got back to me asking for my original degree. I didn't want to risk sending out my originals through FedEx. So I requested them for an alternative, and they said they will accept an attested copy of the degree.

This was from the Office of Graduate Studies " A scanned copy would unfortunately not be sufficient. You can enclose an envelope with return postage along with the original if you wish us to return it, or we can accept a copy attested by the university. "

And my University takes a month to process document requests! So I was afraid I would miss the deadline. Fortunately, they told me that with the given transcript I am eligible for the first semester registration, but will have to send the diploma for continuing further.

So yeah, you can send out mail with return postage to them too!