ACH payment interface to Receivables

We are looking for viable solutions to integrate 3rd party ACH payments into Receivables

so far, we've explored

BAI - not an option for 3rd party
Lockbox file - not an option for ACH
Insert directly into EC tables - not an option, we could not bypass the lockbox fields - cannot be NULL
Insert into the exceluploadfordeposits tables- not ideal but appears to be the only light.
EDI - seems cumbersome as well

Any other ideas - ideally, we want to load into ECs tables