Inviting non-registered reviewers

I’m about to start the review process for the first time. I see that reviewer requests are seemingly only sent to registered users in the OJS-system. Since this is the first time we launch a review process, we have very few registered users who are candidate reviewers. How do editors conduct such request using the OJS-system? Is it for example acceptable conduct to register the candidate reviewer in the system, enable the option for the reviewer to look at the submission without logging in, and then send the request? Or are these sorts of requests simply handled outside the system using ordinary emails?