There are no standard function available for that.
Accounting entry for transaction key GBB will be depend on your movement type - Account modifier.
You can see the Account modifier is assigned for the movement type in OMWN t-code. As per the account modifier for the movement type, system will determine the G/L account from T030 table with regards to transaction event key.
There are no option to use Customer group here. You can store the G/L account with regards to transaction event key and customer group in a Z table and you have to determine these G/L account by using a user exit.
