In CRM 2011 (not online), you can create custom workflow activity for things that are not achievable using the OOTB workflow.
In my scenario, I want to send Overdue Case Reminder to group of users (in this case - managers) when a case has reached the Follow Up By date.
If you look at the SystemUser, it has a manager field by default. However, I need to be able to send the email to multiple managers.
My idea is that we create a separate Security Role (e.g. Managers) and put all managers in that role. Then we create a custom workflow activity to get all the users in that role and construct an email to notify them when the case is overdue.
Note: for the CaseLink input, I'm using the CRM 2011 Workflow Utilities to generate the Case Link and put it into the Email Description field.
Hope this helps,