maybe this helps a little
when you do the dcc send maybe you can use /set %SendSlot
example:

on *:text:!Send*:*:{
if (%sendslot) {
write queues.txt $nick $file | .notice $nick Added You To The Queue List }
elseif (!%sendslot) {
set %SendSlot $nick
dcc send $nick $file
}
halt
}


then the file has been sent unset %SendSlot
and then get the info from line 1 in queues.txt
to to send the file
"$nick" "$file"
then delete line 1 from the txt file
and the next line in queues will become line 1

hope this helped
i didnt really understand what you meant by this though:
the 3,6,9,12 sentence move to the 1,3,6,9 and the 4,7,10,13 will move 2 the 2,5,8,11th line