I tried a few starting points but eventually worked from this:
This does not support multiple endpoints, but that is definitely the easy part. This driver has a range of options for changing reporting interval which are based on the Zigbee cluster standard, but they seem to do nothing on this device. Either they don't implement the standard correctly or I am missing something. This applies to the built-in driver (Generic Zigbee Outlet) as well.
To be honest I have no idea what to do here. Several approaches to setting this reporting seem to do nothing.
Edit: I figured out the reporting problem by reading even more of the standard document. The problem was that I was not configuring all of the reporting. Other outlets tend to report things like AC frequency, which this device does not support, and apparently, other devices don't support things like RMS Current, which this device does support. Adding the following line to the power reporting configuration:
cfg += zigbee.configureReporting(0x0B04, 0x0508, 0x21, 30, 900, 1); // RMS Current
Configures minimum 30 seconds, maximum 900 seconds reporting of RMS Current (attribute id 0x0508).
