Enter Negative AR Cash or Zero Cash to Customer Accounts

Currently on 10.0.4, moving to 10.1 shortly.  Trying to figure out the best way to clear out a charge on one customer account against a credit on another customer account.  In our past system we were able to post a negative cash amount to zero out the credit and a positive cash amount to the other account, netting to $0 cash posted.  Epicor does not appear to allow this.  Any help appreciated.