Generally, they open as windows if they specify a size, since Chromium doesn't support MDI (different sized document windows inside the main window). A setting to ignore the size specified for such things should do the job.
I've stopped using O Next, as it crashes after 10 seconds or so. These problems have carried over into the update of the last couple of days. I'm wondering if it wasn't my trying out several speed dial extensions at teh Chrome extension store, as it was just fine before this. But uninstalling everything, including personal data, hasn't stopped the crashing, so its most likely not the extensions goofing up (especailly b/c I uninstalled them).
At any rate, O Stable is fine, so no worries, but I'd love to try out the Next build and send the test info back to Opera....but not if its crashing all the time.
I think it isn't possible.
The closest thing to this is the command line switch "--user-data-dir" but that will share the whole profile (cookies, history, session, bookmarks, etc).
E.g. this is in the Opera shortcuts, should be set to:
"C:\Program Files (x86)\Opera\launcher.exe" --user-data-dir=\\server\path\to\profile
I don't even know how you get this to work before if hypothetically you ran 2 different Operas handling the same file at the same time. I believe it'd give instant errors.