How to add sort by "quantity" for product list?

[dunngra]

Hi there,

 

Would somebody be able to help me with how to add sort by "quantity" onto the "default order by" options for product preferences?

 

I simply want to be able to default any product list to display the items with the highest stock levels first in descending order.

 

Many thanks

 

P.S I'm using 1.4.9.0

Edited November 13, 2012 by dunngra (see edit history)