Dawn,
You could use the
Delete Lead filter to delete them from your Marketo instance, but be sure to keep Remove from CRM = False, since you don't want to remove them from Salesforce. You will lose information about any visits to your website or landing pages in Marketo, but if that isn't important to your recruiting team or company, it shouldn't be a problem.
Also, this should only be set up
after the permissions for your Salesforce sync have been changed to no longer sync over those candidate records. Otherwise, those records will just come back in Marketo during the next sync.