instead of using $50 $49 $48 etc you can use $1- which will return every token, and since this only goes up to $50 this wont work if the message is 51 words long

on *:text:!backwords*:#:.msg # $backwords($$2-)
alias backwords {
  var %a = 1,%b
  while ($gettok($$1-,%a,32)) {
    %b = $instok(%b,$v1,$0,32)
    inc %a
  }
  return %b
}