From the XDA forum, to assign your Bluetooth Headset button to Voice Command,

1) Install Microsoft Voice Command
2) Download a third party registry editor like Resco
3) Navigate to HKEY_LOCAL_MACHINE\Software\OEM\VoiceCommand and set the “Path” value to “\Program Files\Voice Command\VoiceCmd.exe(without quotes) (originally it might be\Windows\sddialer.exe)

For mate KJam or Jasjar, there is free tool to do the same
Link- http://www.burling.co.nz/files/VoiceEnableSetup.zip