Isn't that trivial in a sense? Encrypt with layer 1, then use that encrypted channel to send layer 2 (and so on). Not sure about the performance.
Signal has a post about using pre and post-quantum together: https://signal.org/blog/pqxdh/
> The essence of our protocol upgrade from X3DH to PQXDH is to compute a shared secret, data known only to the parties involved in a private communication session, using both the elliptic curve key agreement protocol X25519 and the post-quantum key encapsulation mechanism CRYSTALS-Kyber. We then combine these two shared secrets together so that any attacker must break both X25519 and CRYSTALS-Kyber to compute the same shared secret.