Those invites are tied to your account so I am not sure if you can share them.
One thing you can try is to hover over the "Use It" and see if the url shows a randomly generated code (XXXX-XXXX.. etc.)
Then you can send the person that code and they can use this url to claim it. Again, not sure if itll work. Only other way is to give up your account to someone else (ie. remove all your personal info and give them your account and they can change the password etc to protect their info. More difficult if you had placed an order already on the account as your address will be shown.)
Code:
https://account.oneplus.net/invite/claim/XXXX-XXXX..