There is no easy solution for this at the moment and there is no real alternative on Mac OS X either,
but you can just forward the X output from the server to your Mac OS X via SSH and the -X option:
ssh -l USERNAME -X virt01.ams1.gosi.at
After the connection was established, just run virt-manager from the console. The window of virt-manager will popup on your Mac OS X screen.