I asked the earlier this week, and apparently InterDiscount (http://www.interdiscount.ch/idshop/index.jsf) does developing. The girl behind the counter said so, and I saw a little drop-off desk. I have no idea how it (if?) works, but I will be checking.
I've heard MIGROS does, or did, developing, but I'm not sure about now. I'll need to check into that, too.