One technique I know helps is to lift our head just a bit and try to relax as you go down. This will open up your airways to the maximum and also leave more room for your vocal cords to vibrate freely (the lower frequencies requires larger movements of the vocal cords). Just be care to not raise your head too much; If you raise your head too much, the vocal chords will stretch, and you will get the opposite effect. You need to find a perfect balance here.

Note:
In the other end, when you go up in the frequencies, lower your head so you chin gets closer to your chest. This will help you to be more accurate in hitting the right note when you go up.

One technique I know helps is to lift our head just a bit and try to relax as you go down. This will open up your airways to the maximum and also leave more room for your vocal cords to vibrate freely (the lower frequencies requires larger movements of the vocal cords). Just be care to not raise your head too much; If you raise your head too much, the vocal chords will stretch, and you will get the opposite effect. You need to find a perfect balance here.

I'm not sure if this technique will give you a whole note more down (it will probably give you some improvement), but it will certainly improve the performance and strength of what you are already capable of. And sorry - to do it well, you need to practice...