From what I understand you to be saying, that you are developing the film in an alkaline developer and then fixing in an alkaline fixer. If that is true, then to use an acidic stop would be counterproductive. The one non acidic stop that I am aware of is water. Several photographers that I have encountered are using water as a stop bath...albeit the developer action will continue until it is diluted to a non active level. This continuation should not be problematic once it is factored into your processing regimen.