A variation of the above was a standard part of the Shabbat dinner coordinator's speech each week at Hillel back in the day. Seared into the collective memory was a set of incidents before my time along the lines of:
Student 1: "...al netilat yadayim."
Student 2: "Hi, I'm Student 2, what's your name?"
Student 1: "..."
Student 2: "Well I never! You people are so RUDE! This is the last time you'll see me here."
Student 1: "..."
So this disclaimer was created in order to stem the tide of students being frightened away from Hillel. As a result, many people picked up the practice of "preserving the continuity", so that they could fit in and look like they knew what they were doing, even if they had no such "custom".
At Hillel and elsewhere, this has led to many conversations in a pidgin of pantomime and telepathy; for example, making frantic salt-shaker motions to communicate "Where's the salt?", or having an extended conversation like:
"Mmm mmm? Mmmmm."
"Mmmph mmmm mmmm."
"Mm! Mmmm mmmm?"
"Mmmm, mmmph mmmm."
Which, of course, translates to:
"I think everyone's here - who wants to say hamotzi?"
"Wait, what about Plonit? I think she's still washing."
"I don't think she wants us to wait for her; we can go ahead."
"She might have gone to the bathroom; let's wait another minute."
"Oh look, she went over to that table. Never mind."
"Was someone sitting in this seat? Should we wait for them?"
"No, I don't think so, they were there for a second and then moved."
"Ok, let's say hamotzi. Who wants to do it?"
"Why don't you?"
"Okay, FINE, if no one else wants to. Birshut..."
One year around Purim, I made a fake event sign, advertising "Preserving the Continuity" by Marcel Marceau. (I never admitted to making that sign at the time. NOW THE TRUTH COMES OUT.)
Back to the present. EAR and I have started studying the Rambam's Hilchot Berachot (Laws of Blessings). It turns out that he addresses this issue in Hilchot Berachot 1:8. Here is my translation:
For all blessings, one should not interrupt with other things between the blessing and the thing over which one is blessing, and if you interrupt, you have to go back and bless again. But if you interrupt with things that are on the topic of the thing over which you are blessing, you don't have to bless again.
How? For example, you blessed over the bread, and before you ate, you said "Bring the salt" or "Bring the cooked dish" or "Give Ploni something to eat" or "Feed the animal" or something like that, you don't have to bless again. And likewise for any similar cases.
So there you have it; these silly conversations happened in the Rambam's time too, and he says that you can just say these things out loud rather than playing charades. Take that with a grain of salt (as it were), but now you have something to rely on.