Thanks for posting this. It can be really helpful for new to grapple or even returning players to know. I would just like to add that the same can also be done with a command while on the server.
Continuing with the example Titan provided above (using the "E" key for grapple) you can open the console (by pressing the ~ key) in game while on the server and type the following into the console and hit enter:
mutate offhand E
Just an additional way to accomplish the same result.