I haven't tried all of the xpra options, but it would be a matter of starting an instance on the remote machine and then running the command to attach to it in the local machine.
I suppose that you could start a terminal session on the remote machine and spawn GUI applications from that. I'm not sure if xpra allows for a terminal session directly from the command line though.
Right now the workflow is simply ssh -X machine and then run some scripts that may or may not open interactive windows and then look at the result files using some graphical application. The same as if I was running it locally really (except on a beefy machine)..