From a sectional this weekend. Playing with a friend, whose cue structure is very similar to mine, but with a few small tweaks.
The actual hand:
3S(two top spades)-P-4D(courtesy, not club Ace or KQ)-P-
So far, easy. Bid Exclusion RKCB, right? No. Partner has already denied the club Ace. With this specific structure, 4C would show the Ace, or the KQ. But, bypassing the 4C cue means no club Ace. Hence, Exclusion is off. This illustrates why. You don't need it. The 4NT answer will tell all.
Next, change the hand slightly.
A better hand, but more difficult. Same auction, up through 4D.
At this point, this partner likes 4S in a heart sequence to be a general slam move requesting partner to start asking questions. In other words, a desire to answer rather than ask.
However, "surrogate RKCB" works.
This is a method where a call that cannot be Exclusion inferentially (because of a denial or promise earlier that resolves all questions and therefore makes Exclusion redundant) takes on the "most useful meaning" by default rules.
In this sequence, the "most useful meaning" is obvious -- RKCB, but show the SPADE king and queen rather than the heart king and queen. Opener is looking at the heart king and queen and therefore knows that answer. But, the sequence is such that Responder could never cue spades. The 4S relay to answer won't work, because Responder won't guess 5-7-1-0.
So, 5C becomes RKCB, spade focus as to answering, heart focus as to strain.