You can do that, but you will get better results with a light. Is there any way for you to hang a shop light from the ceiling? Perhaps put them on a table in front of the window, with a shop (or what ever size fluorescent light) hanging over them. I don't get enough dependable natural light, even in a south window to be very successful, but it can be done. One thing that I've done in the past, and it helps tremendously is to make a tin foil lined box for them to sit in. It helps to catch all of the light coming in from the window, and re-direct it back onto the seedlings. Be sure you start them someplace warm, then get them into the light right away... as soon as a few seedlings have popped up. It wouldn't be too hard to pick up a light fixture, and mount it over the tin foil box.