Genie client and SHEF "poweroff"

I cannot get the poweroff keypress to work for a Genie client (C41) through SHEF. The poweroff keypress works for the Genie itself, and other keypresses work for the clients (e.g. pause). I imagine this is just DirecTV doing a half-implementation of SHEF on the clients, but I thought I would post to see if anyone has a trick to turning off Genie clients via TCP/IP.

Thanks for any feedback!