Can you add a mechanism to input referral code at sign up?

Currently referral is only attributed it they sign up through the link. I have referred a couple people that signed up by coming to the site and logging in via lightning wallet. There is no way for them to attribute that referral to me.

Not a big issue. I am sure the overwhelming majority of referrals are done via link but would be a nice to have feature if when someone signs up without a referral or invite link they can attribute the sign up to another stacker.