Parker,
You can always add people to the campaign in batches. You could approach it by geography, by time since last communication, by their lead status, etc, etc. You could even batch them by first letter of their last name (that's pretty random).
If you truly wanted randomness, you could create a smart campaign with the smart list of everyone who is NOT part of the engagement program. Then in the flow step you can pick random 10% (or higher depending on the #'s) of the list, and send them to the engagement program. Then add a wait step of a few days, then add 10% more, and so on.
Hope that makes sense and is helpful.