If you are just going out for conditioning why even pack any real gear? I would just get a few 5 pound sacks of flour that add up to your total gear weight and pack that around. No point in wearing out any gear. Repeated packing and unpacking a sleeping bag does wear it out. Keeping it under compression weeks at a time is not good for it. If your bag has a special fabric coating (like dry-loft), each time it is packed up it wears creases in the coating.

Why do you think your Megalite was packed in a tight bag for a month? I doubt this is the case. They pack them tight for shipping because shipping costs depend on weight and size. Actually when you buy a bag directly from Western Mountaineering they often do not even make it until you place the order. They would not damage their bags by keeping them tightly packed for much time. If you go to REI you will also notice that the sleeping bags are stored in the larger cotton duffles.