So, how and why? Just because you can generate in an offline computer it doesn't mean it's secure.
Then what is 'secure'?
AFIAK cold storage is the best option and is very secure. Cold storage is done in an offline computer, does that mean it isn't secure? 
You didn't understood correctly what secure is. If your peovate key is never exposed to internet, how can anyone steal the private key? Reused R values are a problem but it is different matter. Please understand what it is, what you are hoing to tell and then post the correct one.
-MZ