I know it probably won't be as fast but you could open multiple browser
windows with WorkFlowy and tile them in whatever way you like, so you
could emulate a Brainstorm environment (probably a screen positioning
utility like WinSplit Revolution could make the window positioning a bit
faster).

Just tried this with a couple of tabs.
Doesn't really work, since the tabs aren't being updated in real time.

One of the cool things about Brainstorm is that the all the panels are updated as soon as you make edits.

It really makes me think if there's a market for a Brainstorm-like software that's cross-platform.
Market's probably too small... :)