I'm trying to track referral sources, i get a lot of business from word of mouth and i want to track that and create automations to thank those who give me referrals.

So lets say i have an existing client "John Smith", and he has referred about 15 clients to me.  When i go to those client records i want to be able to see that John Smith Referred them, and when i look at John Smith's record I want to be able to see all 15 clients he referred to me.

Now i think I partly figured this out, but I'm getting stuck.  I edited the contacts module, and added a multi select lookup against the leads module, and created a linking module and it auto created a related list.  This seems to work, as long as i don't convert a lead.  Once i convert a lead the record disappears because they are no longer a lead.

I thought to create a pair of multi-select fields, one for contact and one for leads, however the limit of 2 multi select fields per module prevents that.  If i create a multi select field on the contacts page referring the contacts module, then it automatically creates a related list using up my limit of 2 fields.

Is there anything i can do to preserve this relationship once i convert the lead to a contact?