Render object only on client side?

#1 Depends on the object tbh.
For particle emitters, this is what I did for the IPS Pro:

class loc_ParticleEmitterNode : public ParticleEmitterNode
{
	typedef ParticleEmitterNode Parent;
public:
	loc_ParticleEmitterNode(){ 
		mNetFlags.clear(Ghostable | ScopeAlways);
		mNetFlags.set(IsGhost);  
	};
};

#2 its a physic's object.

#3 Have you tried the above?
I don't know what works and what does not. You should look through the class for any function or code block that is executed on server solely.
The particle emitters don't execute anything on the server of significance therefore I could just create a subclass which was ghost-only.