A mechanical coupling is not that difficult to design. There needs to be no communication between FH and Orion for this use case. It could be mounted with the shield on top to simplify the mechanism. Separation could be purely mechanical, with springs.

> I also don't understand how you plan to re-light the engines on the 3 falcon cores for a second burn (required for the delta-v you propose) and the fuel economics.

Reignite only the second stage. Instead of putting the payload in orbit, put it on a suborbital trajectory with a high apogee, then boost down to hit the atmosphere at the desired speed and angle.

> I also don't understand the trajectory you envision. Even if you could re-light the FH engines and couple Orion to it, I don't understand how you would get the re-entry angle correct.

You have the delta-v - just use it in the right orientation. An Orion is lighter than the payload to LEO of the FH, so there will be a lot of propellant for the boost up and the boost down.

> Regarding the mass simulator, it's not clear by your description how the shields would be tested in that scenario.

The shield doesn't care what's inside the Orion - it cares about mass. You might need some attitude control (you can use flywheels) and parachutes if you want to recover anything, but all the rest is optional.