Importing Images without PID

Hy,
We have a facility which sends studies to the server without PatID to the server. The server doesn't import the images looking at the PatID(which is 0 in all in-comming images).I know I could configure import converter to import the images and replace any DICOM tag with existing DICOM tag. But I want to do it little bit differently.
I want to configure Import Converter such a way that I can import studies in to the server when there is no PatientID defined (its all 0000) in all in-comming images. I want to define it such a way that before import converter Auto Assigns any PID it looks up the database for atleast PatNam and PatDOB or any other parameters to see if there is patient with the same parameters existis, if it does the import converter should just add this new in-comming study to the existing patients other study with new accession number, But if the patient does not exist, the import converter auto assigns PatID(n+1, where n is the last Auto Assigned PatID) and auto assign accession number(n+1, where n is the last Auto Assigned Accession number) to the new study in chronological order.Is this possible?Thank you.
Any help to script this will be appreciated.
Thank you
Dave

Thank you for reply Marcel,
When you said some external program are you reffering to may be a external VB script?
Do you think the following VB script will pull of the job if called external?
PatientID = Nz(DMax("[PatientID]", "DICOMPATIENTS"), 0) + 1.
If yes How do I call external Scripts from Import Converters?
Thank you