Create Projects and assign users to projects with SOAP

we would like to create projects and to assign users to these projects by using the SOAP-webservice. While creating projects seems to be quite easy, we do not know how to add users with a specific role to a project. Since we have to manage many projects with many users it will be a big benefit for us, if we could use a Template-Excel-Sheet containing the users and roles and create the needed assignments automatically via SOAP.

Is there a way to do so by using the webservice or is the only way at the moment to assign the users manually to a given project?

Thank you for your reply.

Best Regards,

Holger