Rico Suter's blog.

PlayTo is a great technology which provides the ability to play the current video or music from your tablet to your TV. The problem is, that most devices, for example a HTPC running XBMC, supports PlayTo but is not certified. However there is a way to simply disable this restriction and use non-certified devices as PlayTo receivers. The reason why this is not enabled by default is that these devices may not work properly.

I tested the feature with XBMC and it works without problems - even better than with my Xbox 360 which is a certified PlayTo device. To enable uncertified PlyTo devices, you only need to add a key to your registry, install your device in the Windows 8 settings and send the video to your TV using the charms bar. Under HKEY_LOCAL_MACHINE\Software\Microsoft\PlayTo add the key ShowNonCertifiedDevices with value 1 and type DWORD (32-Bit). Or simply open the following RegEdit file:

The PlayTo_ShowNonCertifiedDevices.reg file to change the registry:

Windows Registry Editor Version 5.00