A matching X25519 public from non-clamped Ed25519-public and Ed25519-secret

Question

Given an Ed25519 key pair, can you think of any way to get to the same X25519 public key from the Ed25519 secret as from the non-clamped(!) Ed25519 public key?

Ed25519 secret
    \=> Ed25519 non-clamped public
            \=> X25519 public (transported)
            v^ should match 

        /=> X25519 public (generated)
/=> X25519 secret (transported)

Ed25519 secret

My Stackoverflow question has some libsodium calls for further illustration.

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What about the inverse:

X25519 secret
    \=> X25519 public (generated)
            \=> Ed25519 non-clamped public (transported)
            v^ should match 

        /=> Ed25519 non-clamped public (generated)
/=> Ed25519 secret (transported)

X25519 secret