I am not sure your key looks the same as my 95's. I can put a key chain on mine. I have a MB three pointed star key chain but no keys on the chain.
It is not advisable to put keys with you car key as the weight will damage your ignition switch. Do a search on the forum and there have been plenty of discussiona on this topic. So MB is doing you a favour so you don't have to end up paying $$ to replace your ignition switch.
04 Infiniti G35.5 BS