Another way of doing it which is great when you have more than one instance.....but more applicable when you have 3 or more....
Create a Non Persistent Business Object that has as many Reference Attributes as you need... For example.... assume you need to bring 4 different instances of a BO into context to do some comparison or whatever.
Create NP_My4BOs with ps_Instance_1, ps_Instance_2, ps_Instance_3 and ps_Instance_4. Injected each of your instances into the Reference Attributes and then you can pass the NP BO between any Processes and it takes all of the instances with it.