Assignment by least busy in BPM


Currently our customer uses a BPM-process for Round Robin-assignment of cases. This is due to the fact that they have a specific team that handles their cases. 

Now they would like to change the assignment process to assignment by least busy. Which is possible in the settings for inbound emails, but then the cases will be distributed to all users. Is there a way to set up assignment by least busy by a BPM-process?

Best regards, 
Frida Yngve