If what you want is output then you could use the -o pipe facility 
(certainly on linux) to send raw output to lame.
   Licencing considerations meanthat really we cannot incorporate MP3 
directly into csound.  A sufficiently clever programmer (SCP) could create 
an rtaudio module to create mp3 files, or could create a mp3out opcode as 
a loadable code; we just could not distribute that via sourceforge.

==John ff

Perhaps it will help if I remark that the SCC (Sufficiently Clever
Compiler) never got wrtten either!

==John ff
> Thank you root!
>
> Such a pity that I'm just a NSNCP! (Non-sufficiently non-clever
> programmer).
> (Hmm... Was that double negatives?) (You see what I mean... :-)
>
> Jonas