It turns out this feature is available from iMON software (I have a Windows Media Center IR receiver, IR310, using Soundgraph iMON drivers).  Under windows commands, power tab, one can simply assign a button to log off.  I assigned the red WMC remote button.  Now, I am using an MX-880 and it's pre-programmed support for WMC, while good, did not include the red, green, yellow and blue buttons.  So I had the MX-880 learn these using a WMC remote.

The result is a very nice solution.  By assigning a macro I can press one button to turn on the TV, amplifiers, and log in as well as do the reverse, logging out when I am done using the HTPC.  And because it is RF (repeating to blasters stuck to the components) there are no "misses" with line-of-sight IR signals.