Create production version with each alternative BOM, e.g. VER1, VER2..
Go to OPL8 make setting automatic selection of production version. So your production order selects VER1.
Go the info-record and assign VER2.
OR
You can go to OS33, change the value to BEST
Go to OS31 create a new selection ID or change an existing Selection ID make a usage "universal" as priority 1.
Go to OS30 assign the selection ID to BEST.
And create your subcontracting BOM with usage type as universal.