Here's another awk solution (different strategy, and slightly shorter when compacted - Update: this reverses every line, and if your's did the same, i.e, without the END block, it would still be shorter than this...oh well):

#!/bin/awk -f
{
  for (i=1; i<=NF/2; i++) {
    t=$i
    $i = $(NF-i+1)
    $(NF-i+1)=t
  }
  print
}
[download]