Create part requirement using web service

Summary: We would like to create a part requirement against a 3rd party document number.

Content (required): We would like to create a part requirement against a 3rd party document number. I found an API to manage part requirement lines but it seems that parent entity ID (Header ID) is mandatory while creating a requirement line and there is no way to create a part requirement header using APIs. So is there no way to use APIs to mange part requirement without a manual step to create part requirement header using application.

Version (include the version you are using, if applicable):