Khaled,
There is absolutely nothing a young accipiter can learn from a baggie that cannot be taught without one. You can use a small toy on a string to teach him to foot and fight with prey. Or roll a small ball along the floor for him to play.
After my first imprint accipiter, I generally stopped giving baggies all together because I didn't like how long they suffer with young eyass hawks and I realized I could teach those lessons - which are very valuable - without resorting to them.
I should also note that I focus on ground game, so I have not figured out how to use a lure substitute for flying quarry, and that I have occaisionally used free flying baggies to teach that, but only when the eyass is flying strong.
I look forward to reading the progress of your project on this thread BTW.