Use a Design Pattern: Proxy Item to put on your sitemap and use a Mappings to make the two buttons and a Rule to forward the command to the right Switch.
Switch FF_LivingRoom_LivingRoom_TvVolumeProxy "Volume"
rule "Tv Volume Proxy received command"
when
Item FF_LivingRoom_LivingRoom_TvVolumeProxy received command
then
if(receivedCommand == ON) FF_LivingRoom_LivingRoom_TvVolumeUp.sendCommand(ON)
else FF_LivingRoom_LivingRoom_TvVolumeDown.sendCommand(ON)
end
Switch item="FF_LivingRoom_LivingRoom_TvVolumeProxy" mappings=[ON="Up", OFF="Down"]