How do I handle baffles at the corners on a hip roof?
First off let me say that I am not a professional insulation installer. But I can tell you that the idea with baffling is that it is supposed to allow a space for air to flow from the soffit along under the roof sheathing to the open air space above the insulation fill level. From looking at the baffle that that you have installed so far (along area in the red box below) it looks like the baffle goes all the way up to the hip rafter. 

I believe that you will need to work out an air channel along the hip rafter in these short stub rafter openings that allows for air flow. Since this may well span across several of the stub rafter openings before it gets above the insulation fill level that channel will have to be able to be lower than the bottom of the stub rafter upper chord so as to allow air flow from the lower level opening to the next higher opening. Such air channel would have to be done along both sides of the hip rafter. Once this channel is provided for it can be extended down to the openings I have shown in the yellow ovals. 

 

You may be able to then reach into these corner openings and put some baffle material but it would need to low enough down that the upper portions of the openings in the yellow ovals are open. Alternatively it may just be easier to hand pack the insulation in those corner spaces and just not allow it to fill over top of these openings.