There are some bird feed fillers that might do the job.
Here's a picture of one sort of like the one I have and had in mind:
http://www.backyardstyle.com/shop/index.php?page=shop-flypage-10249
Susan
gosh for $5, that's worth looking for at the local feed & seed store! There's one near me that has a huge bird feeder & accessory section. I'll be checking that out. Someone's sure to lose the fancy doodle bean scale scoop (umm, prolly ME) at our shop. Good to know a simple, cheap replacement is just up the road...