I think for A123 cells to be viable in a 1p setup, you are really looking at a high voltage system, like about 9-12 cells with a suitably slow motor to match (and esc too). Mounting them is the biggest nightmare for sure, but there are some possibile solutions:
http://picasaweb.google.com/buikpijn...RevoConversion
Something like that, or double stacking them on either side of the chassis in sausage-type configurations. Certainly do-able, but it requires alot of imagination and work.