Do you want record level capabilities or system as a whole? The latter is there for you already via Disable Sync.
The reason why this question has not been answered fo far is because it has been posted to the Champions group and not to the products section. Read here: Getting the most of the community when you have a Marketo question
These 2 articles may help you understand the sync:
To set it up is easy:
Create the fields in SFDC on lead and contact. Let them synchronize with Marketo. Then log a ticket to support to have the filter enabled.