Question: We've seen Light completely manipulating the robber in the bus-accident case (in which he figured out the identity of the FBI stalker). At the end, though the robber died, but everything went according to the book or in other words the robber was completely manipulated. 

So my question is, is it possible for Light to gain absolute obedience over the victim without killing him? If so, why doesn't he utilizes this power? 

One possible way to gain absolute obedience is to write a task for the person and make the person's death to occur after a long period (say fifty years)

Answer: 
There are a few practical limits.

In the movie the death had to occur within 23 days.

In the anime, Light experimented with what he could make the victims do. If it was physically impossible for them to do something, nothing would happen.

Also, remember one of the rules:

> 
> After writing the cause of death, details of the death should be written in the next 6 minutes and 40 seconds. 
> 
> 
> 

That's not a whole lot of time to write down what someone should do. 

Apart from that, the victim would be forced to do what was written, as Light discovered when he did his experiments.

Also, it only seems to affect the target of the death. It was pointed out somewhere early in the anime that others could not be coerced. When Light tried to find Ray Penbar out, he had to create a pretty complicated scenario. He could not just write "Any FBI agent will now reveal him- or herself".
It is possible to make someone do everything that would be within his/her normal behaviour but only within 23 days before the death. What happens in this time also must not kill other persons. 

The correct time you have to specify the actions and circumstances of the death is 19 days if you first write the cuase and circumstances of death and than the name (Rule VIII).

So if you want a clown/ acrobat to perform at you birthday party, showing this and that trick and so on, it is no problem as long as you write it several days early and make him die shortly after this - he will cancle other arrangements and come to your party. Try the same with a monkh and he has a heart attack beacause ha can't ride a unicycle over a high wire while playing trumped.

Or you can write the name of some hundred workers make them revolt and get shot by the police. That should be fine too as long as noone else woud die because of it.