Depending on what you are specifically wanting to accomplish this
might reduce some time bring you closer to a trick. Getting geeky here for a second...whenever considering these simulated activities the most important thing to keep in mind is the concept of "fidelity"; that is, the degree to which the simulated tasks mirrors the actual task. A suspended harness could potentially enable you to refine and strengthen your board off board off grabs, board off kick flips, single grabs, and such. That's probably about it. Anything beyond this may be dangerous. Working on a king dead man for example could be lethal if something went wrong. As mentioned in a previous post, you could probably accomplish this just as easily sitting in a chair and it would be far safer.
The issue with any of these types of simulated tasks is that there is no way to replace moving through the air while having to control the kite and executing the trick at the same time. This is why I laugh when I see people do any type of trampoline training. Sure, it may get you used to going inverted but controlling the kite while being inverted is most important.
Something to consider as an alternative. Instead of training for specific tricks, you would probably be better off spending your time doing physical training specifically for kiteboarding to keep your muscles conditioned and prevent injury. This will probably give you far more return for your time and keep you kiting longer. I see too many people not kite for weeks or even months and then go out for a 2 to 3 hour session and then wonder why they are in pain the next day (i'm more guilty of this than anyone
). So, I started using resistance bands tied that are connected to a bar. Using a strap I tie the bands to a pole (or use a door mount). I can work back, shoulders, core, quads and replicate all the stances used when riding (upwind, blind, toeside, etc). And the best part is that its all very simple and compact so I can take this stuff anywhere. This has been a true game changer for me with regard to activity that contributes to kiting.
Good luck and be safe.