I could do something like this, but this gives me a circular reference because concat requires an NDFrame which imports the format module. Any idea how to get around this? 

```Python
    col_num = (max_cols // 2)
    left = frame.iloc[:,:col_num]
    right = frame.iloc[:,-col_num:]
    sep_col = DataFrame(data=['...'] * len(frame),index=frame.index,columns=['...'])
    frame = concat((left,sep_col,right), axis=1)
```