First, I would be surprised if the BillPay from the BoA individual account to the WF individual account didn't show up as a check in your mailbox. How was the WF account specified in the BoA BillPay?

Second, there is a faster method than your "fast/inconvenient" method. Instead of depositing a check, get cash from BoA and deposit cash in WF. It's more inconvenient, but there's no clearing time for cash.

Your best bet remains split direct deposit. There is no publicly accessible immediate (or even less-than-several-days) funds transfer system in the US.

The only other thing I can think of is a credit card that has associated checks. If you get a credit card that doesn't start charging interest until the next billing period comes around, it could function as your free elastic buffer.