As you'd probably know Marketo allows converting people via the "Convert Person" flow step. But, let's take a step back and understand why you want to convert lead records to contact records from Marketo. Converting a person in Marketo will result in a new account and opportunity in Salesforce. Almost, in all cases, I don't see a lot of merit in having a new account and opportunity records getting created in SFDC on converting a lead record. Please note that even if you're able to convert lead records in bulk from Marketo, this would not change, you'd still end up with a dedicated account and opportunity records for each converted record in Salesforce.
.png)