In a BPM that I pieced together from examples here that sends out an email on DMR action that includes the reason info, I added DMRActn and Reason tables and used them to bring in the reason description. So, the reason code is there on the DMR Action table IIRC.
That this seems straight forward, I must be mis-interpreting your use case and what you need to do. But, since I have been ingrained in this BPM doing similar things it rang a bell to the bit of struggle I had to grab the reason description for the email.