Well I'd save the main image as a png with Alpha map, take it into Photoshop or equivalent and put the backgtround in there!

The other way would be have a strong light coming through the window like you would have anyway and I'd just turn off shadows on the front light causing your problem.
For this scene a point light above the character would work better and if needed some fill lights without shadoe casting!!

Injustice will be avenged.
Cofiwch Dryweryn.