I have also got a dummy cake in one of our local bridal shops, which is displayed in the window along with a sign with my details. I also have several cards inside.
I found that by going in and asking, I got a better response, and the lady was really pleased when I said if she showed me what she was going to display, I would make a cake to match one of the dresses. This then gives them a good reason to put it in prime position.
There is no charge for this, as she has found this helps her window display.
Good luck, and I hope it works well. Let us know.
gateaux de mandy