Okay I found out that there is a simple trick to start pSRO as a multiclient - but using NoDC Client!
To do that, you just need the sro_client.exe patched to NoDC client.
When you run pSRO and you want to start it again you will get this error:
You can avoid that by right-click on the silkroad.exe and click "Run as..." or "Execute as..." I don't know the english translation exactly xD
Select this and press OK:
The Silkroad launcher should start without the "Silkroad is already executed" error. I can launch 2 NoDC clients on 1 PC now. I hope it works for you, too!