You could use the /play command here with the -b switch to 'play' the clipboard. See
/help /playCopy the text to the clipboard, then type
/mpaste. It will be posted to the channels, one at a time, at one line per second, so 10 lines to 10 channels will take around 100 seconds.
(Note that you can still chat normally while this is happening)
alias mpaste {
; make a list of channels
tokenize 32 #chan1 #chan2 #chan3 #chan4 #chan5 #add #chans #here
; /play the clipboard to each channel in the list
.play -b $*
}