As long as you have the machine resources both on client and server side (to hand those many clients parallel), you should be able to achieve it.
Like
TEB mentioned, you can just use SOAPUI_HOME/bin/testrunner and pass your project and different options to invoke respective tests.
Either use multiple command line windows to invoke tests or automate them like TEB mentioned using Apache-ANT tool.
I believe you might either have two objective for this: reduce the execution time or test the server capacity (if this is case, use load test instead).
