The only thing to watch out for when you do a long shutter near a window is that the window might become overblown - this can sometimes work to your advantage for a nice effect, depending on the the angle to the window.
Do you not want to use strobes or do you not have any? Using any sort of soft light on the person's face can help, even if it is a desk lamp (although the light from the window will be bluish and the lamp will be yellow...). Worst comes to worst you can tweak in post-production.
The optimal way to do it (if you had access to lighting and such) would be to use a low key light on the face with a blue filter on it (and probably a diffuser like a sheet of "tough spun"). The blue filter would make it all look like the light was from the window.