Automatically switch Playback device when HDMI TV is off

Question

I Have a PC running windows 7 with 2 Playback Devices:

1) speakers - connected via "3.5 mm jack"

2) TV - connected via HDMI (This is the default Playback Device)

both devices are plugged-in all the time.

when the TV is turned ON, the sound plays via TV speakers and that's OK. but I sometimes want to use my LCD screen and pc speakers, and the TV is in standby, but the playback device is still set to TV! And it won't switch to PC speakers automatically UNLESS I plug out HDMI so PC speakers will play the sound.

Is it possible to switch automatically to PC Speakers When TV is in standby?

Thanks!