How can I sneak in and out of my second floor window?

I know, I know, use the door. I will when I can, but there are cirstances (such as my dad sleeping in the living room some nights) that would prevent this from being possible. There is a window in between the first and second floors that I could climb out of, but I'd really prefer to just go straight in and out of my bedroom window. I got a rock climbing rope, and tried climbing down that, but the shingles under my window got in the way and I got rope burn. I can ALMOST climb up/down using ledges, but there's about a 3-foot gap that I can't traverse (or haven't tried for fear of hurting myself; there's concrete below). Please don't just tell me that sneaking out is stupid, because I wouldn't be asking this if I had any moral qualms about it. So any ideas? Like a variation on the rope trick?