Randomize the list before you drop it in the dialer. This is your best and easiest solution.
Create some sort of custom function in ICM script editor which will mark every X call and send it to an agent while all the other calls get disconnected. I don't recommend you do this, as it would get very messy very quickly and it will not give you exactly what you want due to the fact that they are outbound calls and thus far more erratic.
