I'd recommend using Textile, you can then add a paragraph style (poem) to the paragraph, and when converting, in the extra CSS, add a poem style.
Put this in a txt file, convert with
Txt-Input -> Paragraph style - Off
Txt-Input -> Formatting style - Textile
And use the ExtraCSS in the Look and Feel->Extra CSS
Code:
Here's a few lines of a poem in a 'poem' style.
p(poem). 'Twas brillig, and the slithy toves
Did gyre and gimble in the wabe;
All mimsy were the borogoves,
And the mome raths outgrabe.
And now back to normal.
Code:
.poem {padding-left:10%; padding-right:10%; text-indent:0; text-align: left; font-style: italic;}
Adjust extra css to suiit.