Is weighed multi-sig wallet possible?

In a multi-sig wallet, each of the public keys is unique. Is it possible to create weighted multi-sig wallet, such that one private key has more power than the others?

Case 1: typical Example (need 2 of 3 to spend):

2 PubKeyAlice PubKeyBob PubKeyChris 3 CHECKMULTISIG

Case 2: Duplicate public key for weighted signing (need 2 of 4 to spend):

2 PubKeyAlice PubKeyAlice PubKeyBob PubKeyChris 4 CHECKMULTISIG

In this case, Alice could sign on her own (she has 2 of 4), or Bob and Chris can come together to sign.

Case 3: No duplicate public keys, but multiple public keys controlled by one person.

In this case Alice would control two private keys, and then the wallet would look like:

2 PubKeyAliceA PubKeyAliceB PubKeyBob PubKeyChris 4 CHECKMULTISIG

Certainly Case 3 works today. And Case 1 is the basic unweighted implementation.

Does Case 2 work? Or is there some alternative to make Case 2 work? (i.e. a single Private Key holder has more power / shares then others).

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