OPM GL Allocation Basis management

Hello,

My customer would like to use Expense allocation functionality in order to allocate indirect expenses from GL accounts to items using PMAC Cost type. The plan is to define many allocation codes for three different companies, differentiated by accounts and cost centers but the issue is that due to the relevant number of combinations of GL allocation code it's not possible to manage manually allocation basis by item and organization either using allocation basis by fixed percentage or by gl allocation balances (our preferred method using statistical account). Could you please recommend an approach in order to avoid to maintain