built-in property for project directory

I would like to create a DataSource with a File in the same directory as the project, then use a property ${proj_dir}\myfile.xls.

I could create this variable globally, but since we are sharing this project between several developers the directory changes and it would mean that potentially each developer would need to change the value each time they download updates from the tester.

I was hoping that there were some built-in variables in soapUI pro that I could use. I could not find any.