I have to start by saying I love your bears.
In my experience with polymer noses, a really good glue works very well. You could also put a wire on the backside but that might create pressure on the polymer clay and it could break free. E6000 glue is very strong glue. Also Magnatac Glue is iron clad. I have tested it mysel by really pulling on a finished, glued-on nose. They stayed put.
Hope this helps.:D
It took a while for my hubby to see this 'bear thing' as something very worthwhile too. Now he really enjoys seeing what is next. Since he is a dairy farmer , I made a very large Queen Cow sitting in a throne. He has placed her high on a plant shelf in a place of honor.;)