Select the Marketo only person (Microsoft Type is empty) that you want to create as a contact in Dynamics.
Click Person Actions and Microsoft, and select Sync Person to Microsoft.
Click Sync As and select Contact. Click Run Now.
The new Lead record is created in Dynamics. Marketo then qualifies that Lead record into a Contact that is not associated to any Account in Dynamics.
Now, you can select Contact when you use the Sync As constraint in a smart campaign filter.
That's all there is to it!