Notion: Avoid creating 'duplicate' database items with same two custom relationship field settings

So, this is a little bit complicated, and all happening inside Notion.

I have configured a scenario that once a new database item is created in DB1, for all items in DB2 that have a relationship set to the new database item from DB1, a new item in DB3 should be created, with relationships pointing to the new item from DB1 and the related item from DB2. (To make it more visual: Once a new Campaign has been created in my Campaigns database [DB1], for all Contacts from my Contacts Database [DB2] that I have set a relationship to my new Campaign, a Lead should be created in my Lead database [DB3], with the first relationship set to my newly created Campaign, and the second to the Contact I have related to the new Campaign. So if I created a Campaign ‘Free Willy’ and chose ‘Mickey’ and ‘Minnie’ as contacts for this Campaign, Make will create a new Lead each for Mickey and Minnie in my ‘Leads’ database, with relationships to the ‘Free Willy’ Campaign and to each corresponding Contact.)

Now, if I just run it once, all is fine, and all Leads are created. But if I already ran it halfway through picking my Contacts for the Campaign, and run it again after I added x new Contacts, the automation would create new database items for all the formerly created Leads.
On the create-new-database-items action for Notion, I couldn’t find any possible filter, but is there a way to check first if there is already a Lead (regardless of its name or other properties) pointing to both the current Campaign and the same Contact, and then only have Make create database entries for all missing Leads? So if Mickey and Minnie already have leads in ‘Free Willy’ from my first scenario run, they won’t get re-created in case I added ‘Scrooge’ as a Contact to the Campaign and ran the scenario again?