That's a good idea. I always said my memo but then someone told me it was illegal for comp. So I just did all my solves without talking. Not too bad.
It's an interesting question whether or not it's illegal for a competition. There's this rule:
A5a) While inspecting or solving the puzzle, the competitor must not communicate with anyone other than the judge. Penalty: disqualification of the attempt (DNF).
but I could see a claim that you're saying it to the judge, or you're saying it to no one in particular, so you're not actually trying to communicate.
Then there's this rule, which is probably more applicable:
2k) The WCA Delegate may disqualify a competitor from the competition (i.e. from all events of the competition) if the competitor:
... 2k4) Interferes with, or distracts others during, the competition.
It's probably reasonable to argue that saying memo out loud distracts others, and so qualifies for this. If so, it's pretty serious - it would disqualify not just your BLD solve, but the whole competition. I guess I would argue that, since most BLD competitors use ear protection of some sort to block out noise, relatively quiet recitation of memo probably shouldn't qualify as a violation of this rule. And if it is a violation, in many cases I'd think you could disqualify lots of audience members for talking among themselves during BLD events.