You can use the send email action on the person record. Just find the person in lead database (not in program membership view, though as it does not allow you to make marketing actions), then select action Marketing/Send Email. If the email uses the member URL token, it will be populated.
If the person is having issue getting emails from Marketo (because Marketo is blacklisted by their company email server), then you can use the send alert function to send the confirmation email including the personalized link to your mailbox and then forward it to the registrant, which would avoid the Marketo blacklisting hurdle.