Unbilled Receivable Auto Accounting rule based on event type

I wanted to create AA rules where the unbilled receivable account can be derived based on the event type selected. I created a rule to that extent as well.However, when I try to assign this to the Unbilled Receivables account under Revenue and Invoice Accounts function, it wouldn't let me select the rule.

I saw this enhancement request on metalink (1499592.1). Does anyone know if we can do this now? If no standard functionality available, any ideas on what customization we can do as a workaround?

We are on 12.1.3.

Thanks,
Sesh