Open the window. use a hot-glue-gun, or a clamp, or whatever to position it OUTSIDE the window.
Then, get a hunk of foam rubber, and close the window on that to keep the rain out, etc. (this is assuming you're unwilling or unable to drill a hole in the window frame...)
Then, if you want to get REALLY fancy, get another pi, and another rtl-sdr, and put another antenna on the outside of the window on the OTHER side of the house...
I know, I know, shear insanity.
I am wondering where to position my antenna in the attic.
I just moved it there from a windows facing westwards, it now it sits in the middle of the attic, ca 1,50 from the top of the roof, pretty much in the center of the whole building, which is rectangular. The reason for this is that on either side is a relatively small windows. This way, I thought, it can "look out" of both of the windows.
Now get a lot more positions and planes from the East, but I am wondering if it might make more sense to
a) put it as close as possible to the top of the roof, even if that means that there is no line of sight out of the windows
b) put it away from the windows, closer to the gable, so it is close to the outer walls/roof on three sides?
I could try this out and maybe I will, but I also would like to have a better theoretical understanding why one of the locations is better than the other.