First, the best place I know for Sirius info is
Sirius Backstage.
Now, you might not need a view of the sky if you are located in or near a large city with a repeater. If you can get the antenna near that window or even out side that might be enough. If you don't have a repeater in your area, you might be out of luck unless you can arrange to have the antenna installed up on the roof or somewhere where it can see the satellites. Don't forget that the Sirius satellites move through the sky and you'll need to account for that.
You can purchase an antenna extension kit, I think it gives you 50' of wire. I've also heard that using a car antenna might work better as they are less directional than the home antennas. I hope that helps!