40 GbE External Metallic Loopback Plug?

Hi all,

I have a customer using this Mellanox cable:

Mellanox Breakout Cables 40GbE to 4x10GbE usage and configuration

and they need to provide temporary metallic loop-back, at the PCB connector into which the 40 GbE end of the above connector normally inserts, for debugging purposes.

Does anyone know of a loop-back plug, made by Mellanox or anyone else, that can provide this?

Thanks!