Crap, I just freaked out. Thought I was on a conference call!
I can't tell you how many times I have just said yes we can do that, knowing that in 2 minutes they would forget what they even want!
Or said my all time favorite line-Lets take this off-line and discuss it.
If it ever happens you can tell them it (what ever it is) will never work and they won't be embarrassed.