IoT Sitewise - Setting Custom Message Attributes on Alarms

I am trying to set a Custom Message Attribute on an IoT Sitewise Alarm to indicate which device name is generating an alarm. From what I can tell, the normal usage of the Custom Attribute is to provide a fixed default value like the other attributes on the Sitewise model. If there are multiple devices sending data to Sitewise from the IoT Core Sitewise rule, is there a way to provide that dynamic value as the custom message attribute. Here is the SQL that is sending the DeviceName to Sitewise on the IoT Core rule:

SELECT clientId() as DeviceName, state.reported.payload.temperature as temperature, state.reported.payload.humidity as humidity, state.reported.payload.VOC as VOC, state.reported.payload.CO2 as CO2 FROM '$aws/things/+/shadow/update'

I tried setting the DeviceName as a measurement in Sitewise, but I cannot link the measurement value to the custom message attribute value.

Thanks!