doquery for DAOs

Hello, I am working on implementing something like doquery that operates on DAOs--that is, something that will allow me to iterate over all the DAOs matching a certain test without consing up all the instances at once. Before I spend too much time on this, I thought I'd see if anyone else has done something like this already, or if there is a simple way to do this with the existing doquery that I have overlooked. Thank you, -Eli