Nightwatch - How to specify number of clients in test file

I want to test some scenario with n clients.

Of course I can specify number of clients as number of environment to run, f.e:

nightwatch --env chrome,chrome,chrome

But, can I somehow specify this separately for every test? Is there a way to specify this in test file? I have tried to modify process.env.__NIGHTWATCH_ENV_KEY in my test file, but it hasn't work (as expected).