Short Sales + Non Primary Residence (2nd, 3rd owned homes)

Is anyone on the board having success doing short sales for homes which are not the primary residence? These can include investors looking to unload their inventory or people who own 2, 3 and 4 homes.

If so, how does the process vary? It looks like the hardship letter is a main part of the short sale, but would it be relevent to these cases.