If you create a new sandbox buyer account, and during the process make sure to disable the addition of a credit card on this new buyer account. Also make sure the balance of the account is zero. Then when you submit payments with this account it will be sent as an e-check and you'll see the pending payment status. Then when it clears you'll get another IPN with the completed status so that you could update your system accordingly.
Another option would be to use the IPN Simulator available in https://developer.paypal.com. It has simulations for sending echeck - pending, echeck - completed, and echeck-failed.
Angell EYE - www.angelleye.com PayPal Partner and Certified Developer - Kudos are Greatly Appreciated!