Just posted this batch file on the AC forum - should do what you want
Code:
REM To start the app in a particular game mode, add one of RACE_ROOM PCARS2 PCARS_64BIT PCARS_32BIT PCARS_NETWORK RF1 ASSETTO_64BIT ASSETTO_32BIT RF2_64BIT IRACING to your shortcut
REM If you want the app to launch the game for you, and be ready and listening for data right away (no need to press the 'Start application' button)
REM ensure that these properties are set:
REM
REM - "[game] launch exe" - usually the path to Steam's .exe file (for some games this can be replaced with the game's .exe file)
REM - "[game] launch params" - when using the steam .exe file, this is used to tell steam which game to run and has the form -applaunch 123456.
REM it can also be used to pass other arguments to the game's exe. In some cases you may need to use the path to the game's launch exe
REM instead of steam's exe in order to pass the command line arguments you want (if you set this to game's exe, remove the -applaunch 12345 part)
REM - "Launch [game]" - enable this to tell the app to try and launch the game (the app will run the launch exe with the launch params when it stars)
REM - "Run immediately" - enable this to tell the app to start listening as soon as it launches (so you don't have to press the 'Start application' button)
REM
REM For example:
"C:\Program Files (x86)\Britton IT Ltd\CrewChiefV4\CrewChiefV4.exe" ASSETTO_64BIT