Negative LA is something that's unlikely to be implemented, mostly because having a creature with more HD than its ECL quickly becomes very tricky to balance and also destroys some of the assumptions inherit in the system. There was a thread dedicated to it but it seems to have stopped.
'Chop off X RHD to make this balanced' is in my opinion the better way of making -0 LA monsters playable, and sometimes I do in fact mention something to that extent when rating a monster. I'll try and do so more consistently.
For what it's worth, the stonesinger would probably be balanced with... about 2 less HD? Maybe 3? I'm honestly just eyeballing this but that sounds about right.