I suggest you to work on "cloning" the existing manufacturer filter. It's quite complicated, but possible. It took to me around 4 days to do it. I've done it some months ago so I don't remember exactly...The only thing I can say, study with much attention on Manufacturer filter. The thing is the same, but obviously you won't filter manufacturers names but other "features" that you'll have to add to your database in a new table.