QuickBooks class allocation

Need to extend the functionality of QuickBooks so that I have the ability to allocate a deposit between 2 or more classes based upon their respective balances of cash in an account. For example, if the account has $30,000 that is made up of $10,000 in Class1 and $20,000 in Class2, and $30 of interest is deposited into the account, it should be allocated as $10 to Class1 and $20 to Class2. If for some reason, a transaction before is modified and the respective balances of the classes are changed, then the allocation amount should change automatically based on the new ratio.