First, no it is not possible to launch the browser using your own custom command line (or tell Test Studio to connect to your manually launched browser). We have a feature request here
already logged in our system to add this. It is not currently scheduled for implementation yet. You can vote for it which will raise the priority in our system.
Second, yes you do need multiple licenses to take the scheduling server approach that Stoich suggested. However you do not need multiple licenses to full Test Studio. You only need one of those plus one or more license to our Runtime edition
, which is much less expensive. You would install the Runtime edition on your remote VM's that will be executing your tests.
The only other suggestion I can make would be for you to write some sort of framework wrapper that would launch Test Studio or our command line runner
using alternate credentials i.e. a programmatic way of doing Run As...