The reason why you may want to play Maj7 double stops on bass, is that it is the way you can comp using shell voicings on bass. This is best explained in this series of excellent tutorials by Chris Fitzgerald (who knows quite a bit about theory...). Chris shows it for double bass, but it is completely transferable to BG.Why do you think you need to play Maj7 double stops?
Sounds like you need to learn some to theory. And not from the internet...