Hey Garrett,
This is news to me and I don't see a way to do it, either. Even if it were possible I would strongly recommend against it. Clarity does provide the user with the overbooking information when the resource is staffed to the investment. Many users are not aware that simply clicking the Add button and selecting a resource is not the entire staffing process. The folks responsible for booking the resource must participate in that process by understanding the policy and ensuring the resource is not overbooked. Clarity helps them quite a bit but, stops short of doing all their work for them.
Clarity is not known for its preventative capabilities. Those are best left to policy and compliance. For example if the policy states that resources are not to be overbooked by more than 125% then Clarity can identify who is out of compliance with that policy. The filter in the Resource Workloads portlet provides for listing resources who are overbooked, such as those who have been booked more than 125%. Jaspersoft resource management reports, such as the Capacity vs. Demand by Resource may also be used to identify overallocated resources.
Resource allocation policies always have exceptions. When those exceptions are not possible then Clarity becomes the culprit and we all know how that ends.
Dan Drees