Participatory Evaluation Forum - Refocus Institute: Participatory Evaluation Before Program Implementation

I love participatory evaluation and seek to use it whenever possible. Recently I began working for a nonprofit, Around the Clock Caring, that helps homeless families. I have been in charge of the organization's entire program development, and like a good evaluator, I started with (ok, am still in the process of completing) an ex-ante evaluation of the potential programs. 

I would like to incorporate a participatory evaluation of the program's parameters with potential program participants, but since the organization is brand new identifying potential program participants is difficult at best. I've been in contact with one of our local referral agencies to tap some of their participants for my evaluation. However, it's hard to get people interested in evaluation within their own organization, let alone someone else's. 

Ideally, I would like to lead this group group of potential participants through a participatory video project that can also, perhaps, be used for advocacy and awareness later on. I'm going to give it a try to see if  I can get any valuable information to help formulate our programs. 

Has anyone else tried to use participatory evaluation techniques for ex-ante evaluation or other kinds of feasibility studies? Has it worked out? Any tips?