Offset mortgage

It would be great if BECU offered an offset mortgage (aka current account mortgage, aka "Australian mortgage").

 

Specifically, what I mean is a mortgage that is linked to a savings account. The savings account would not pay interest; instead, it would offset the mortgage principal. For example, if I owed $200,000 on my mortgage and had $50,000 in the linked savings account, I would pay interest only on the $150,000 difference. My mortgage payment would still be the same each month, but a higher amount would go towards principal (or a lower amount, if I withdrew money from the savings account).

 

This would be valuable to me because it's more flexible than prepayment. Right now, when I have extra money, I have to decide whether to make extra principal payments (and give up the ability to do anything else with the money), or keep the money in a savings account (and continue paying more interest). It would be nice if I didn't have to choose.