The only *fast* but not reliable way would be gambling.
But thats a risk.
Yeah, that's a huge risk, and anyone can afford to take risk then gambling is the best way to multiply your bitcoins in a quick time, totally depends on how lucky you are on that particular day.
Gambling is the worst thing to do, if you have that huge amount of btc in your wallet, then why don't you just hold it, as that would be the best way to multiply your bitcoins in future.
Totally Agree, why to experiment with your bitcoins? If you are holding that amount then try to multiply your bitcoins in safe way, just keep it safe in cold storage, and rest time will take care of.