Trying to figure out this interaction just in case I run into it in the future.

If an attacker can Juke C-3PO's added evade then can R4-B11 force the defender to roll that die? It hasn't been rolled before... and it hasn't been modified either.

Thoughts?

Yup.

C3PO adds an evade result, and adding a die is defined as grabbing an unused die and adding it to the die pool set to the face noted. It's then a die in the pool for all purposes.

It's just rarely relevant, because C3PO is the only way to add a die to a pool at a point where your opponent can modify it. The other ways (e.g. accuracy corrector, Advanced Targetting Computer, spending Evade tokens) all do so after the opponent has modified dice, so the fact that you're adding a die as opposed to a token or result is not really relevant.