Allow invites through url referral

Crossposted from the forum

I would love some way to provide a referral within an url link which that I can post to my webiste whenever I link to PMOG (As I do when, for example, I blog about a new mission)

Currently you can only invite through an email link and you can send the referral code to a friend manually (if you invite an a second email address you own, copy the link from there while remove the email address and giving them that) but it seems to expire after the first time.