It's very simple.  Either the priest's Order include the power to confirm or they do not.  We know that they do because otherwise no amount of jurisdiction of delegation could supply for the lack of power.  So what's lacking, jurisdiction/delegation, comes extrinsic to the power of Orders, and all such intrinsic considerations can be supplied in cases of necessity.

Exact same situation applies to Confessions.  Priest have the power of Orders to absolve from sins, but priest do not VALIDLY absolve unless they have jurisdiction (and are designated, i.e. receive their "faculties").

One of the priests aligned with Fr. Hewko ...

Can't eastern rite priests perform confirmations without a bishop

No that's why I'm asking how do they do it

Precisely my question:

Is the delegation essential to validity?

It would seem so.

Nonsense.

Is Prümmer's Moral Theology manual nonsense?

Is Canon 782 nonsense?
Or what about Hugon's De Sacramentis below? Is that nonsense?

'Accordingly, the Supreme Pontiff does not add a new intrinsic power to the priestly character, but causes the priestly character to extend itself to some act which itself can be performed by a superior power; just as the ear, while listening through the telephone, does not receive a new species of power or act, but extends itself to the object which itself had to be presented and adapted with the help of the instrument.'

One thing I do know about the Eastern rites is that when a priest is incardinated, he receives an "antimensium" (i.e., a "Greek Corporal"), which is very different from the Latin Rite version (which is merely blessed):

Aside from ornate pictures and colors (vs the plain white Latin rite variety), it is consecrated (not blessed) by the bishop, and contains the signature of his bishop, and is the priest's proof of having received jurisdiction from him to perform sacramental acts.

I'm wondering whether, therefore, this is tantamount or equivalent to a tacit delegation to perform confirmations (and therefore, this authority, rather than anything emanating from the priestly character/orders, is what validates their confirmations)? 

[Can an Eastern Rite priest without a legit antimensium validly confirm?]

Conversely, if that much were true, then the lack of delegation in the Latin rite would be invalidating.

Again, just thinking out loud here, not declaring a position.

I think that everything from Prümmer and Hugon definitively close the book on this conversation.