Lock a bitlocker drive:
manage-bde -lock d: -ForceDismount
Auto unlock a drive using a batch file. This has security implications, ensure you do this safely! These all need to run as admin
1: Create an unlock file in C:\ that will be able to unlock the D: bitlocker protected drive:
manage-bde -protectors -add d: -rk c:\
2: Find the new file that was created. It will look like 'C:\123AB123-1A23-78BC-941A-J019014322A0.BEK'
dir C:\ /a
3: Unlock the D: Drive.
manage-bde -unlock d: -rk C:\123AB123-1A23-78BC-941A-J019014322A0.BEK