Is there?

nope, not that I know of.

Hold down "F" (the key to put away your weapons for the console gamers) and press the secondary fire button during the animation. The weapon won't fire when you do this.

Yep, that works, awesome!... I'm finding it a bit tricky to get it to work smoothly every time but I'm currently running around with just my left hand out using blink.
Perfect for my non lethal run, thank's a lot Devil.

I'm guessing this is not an intentional feature.
I hope they don't patch it, I'm sure a lot of people will be very happy to hear this can be done.

Why would you ever need it?

Simply for looks. Cosmetics. Also the constant sword tip on screen could be distracting to some people. It's an aesthetic choice, not a choice grounded in practicality or necessity

Doesn't this happen in the game at one point? During the 4th mission.