Can one pass a specific proprties file to be applied to a project's root node?

We are running a set of tests in misc. environments. For this I have parameterized these tests using a bunch of custom properties on the project level. So, before executing those tests against a specific environment I first always need to select the project's root node, select the "Custom Properties" tab and click the "Load properties from an external file" icon to pull in the appropriate environment-specific ...-properties.txt-file.

I now want to automate/script these tests and I am using a script that reads (simplified): 

testrunner.bat -s ${testSuite} -f ${reportDir} ${soapUI.project}

But in order to fully automate these tests I also need the possibility to pass in the right property-file(name) to be read.

The testrunner's help didn't reveal any such option, though.

I am sure this is somehow possible with soapUI, but: how?