Can I restrict a user's access to a single folder within a project?

A user's access to a project is on the project level, so there is no way to limit their access within the project to just a single folder.  

A workaround to this would be to create the user with a Basic level of access, then create a project and assign them to only this project.  They can then upload, yet have access restricted to a single project. You can then use the move or copy function to move the uploaded files to another project.