I am afraid, I think you need to handle that in your app itself. They probably don't want to expose those IP addresses used by API.

I first, thought that API key limit is per IP Address, but looks like its not, even I try my API with different IP, limit is decreasing.

For No key, its based on IP Address, so if your application is desktop client, you might don't want to embed it for now. 

And if your app is web service like mobile site, you might want to manage IP address handling yourself in the web server.