Home and Business Share Portfolio Transaction

I am trying to enter a share purchase where the funds used to purchase came from an account other than the linked chequing account. When I am entering it in the "Investing Account" ledger, the account where the funds have come from is already entered and it can't be changed. The account is one of our "Personal Cash Flow" accounts which is linked as the chequing account but the funds for the purchase came from another of our "Personal Cash Flow" accounts. Any ideas what I can do to enter this purchase?