I don’t see any way to sell that.
The idea would be that the Robocop footage shows them working on Vader. The hard part is integrating the two. I can add some Vader lines over the Robocop footage to help, but the real problem is the very dark ROTS footage vs. the very light Robocop footage. I’m not sure color correction can really help with that.
Perhaps it’s one of those cases where the joke is too good to worry about the inconsistency.