Could your SFDC admin set up a wall that until a specific field is filled in the lead won't sync to SFDC?
In our system, without a company name, the lead won't be passed on to SFDC and therefore, the sales reps. When the fills out a longer form with the company name as a required field, then the lead will be passed on to sales.
You could create a new field "First to know campaign" and when the leads are done with that campaign, set up a flow action to mark that box and then sync the lead to SFDC.
Good luck! Let us know what you decide to do!
Liz's suggestion will work. SFDC prevents new leads that are missing LName, FName, and Company. I know some systems have a list of fields that need to be filled in before the sync from Marketo will work.
I normally setup a series of Lead Queues that are only accessible to Marketing:
MQL (sometimes useful if you need someone to vet leads first)
Then I make sure SFDC assigns leads to Nurturing when created. Marketo can be told to sync any new leads directly to this Queue or to use the Auto Assignment rules--as long as auto assignment is set up properly.
Another apporach is to setup a new record type for leads (Marketing Only) and just force any leads created that need to be hidden to sales with the new record type via Marketo. Then update Sales SFDC profile to not have access to leads with Marketing Only record type.
If you ever want them to be visible just update their record type via Marketo using a smart campaign or manually and Sales will be able to see them.