Suitable hybrid encryption approach?
That is right, but is it possible that the victim send me his encrypted symmetric key and I will send the decrypted key back?

I have not personally written any ransonware, nor have I examined how they operation; however if I were to, that is what I would do - once the victim has paid up, they would send a copy of the encrypted symmetric key, decrypt it, and send it back to them (so that the various files could be decrypted and restored).
Since we would never send the private key to the victim, they could not share it (and hence the concern the article you reference would not apply).