I dont advise people as Im responsible for my plane and the other person is responsible(or irresponsible) for theirs...When it comes to ATC there is wording where you can request, or require, but thats not really on topic.
If i were to see someone edging onto the runway, or making their enter/backtrack call while i was on final, i would immediately get in touch and re tell them that i was on final or short final and perhaps ask them if they were aware of my position.If you are on final they are not meant to be there(unless they got out there earlier) so a few things could be happening(they could be on the wrong freq or complete nuffers or anything in between)..
After that point if they continued to line up and still didnt wake up, i would go around keeping to the right hand side of the runway to keep an eye on them. I would also make them aware of where i was if i felt that they werent switched on to the situation
I dont know where your at with your flying, but when i first started flying the radio kind of freaked me out, but as ive gone on i try and communicate early and clearly particularly if i feel i might be in a similar position to another aircraft and am not visual..i tend to do it by stating my position height intentions etc and at least getting in touch. But as far as i know i cant, and its not helpful to try and get them to change what their doing.If its really dangerous, get the callsign if you can and report it, or if you know who it is have a quiet chat about it later on the ground, but first of all make the adjustment to avoid possible problems while you have the chance and are in control of the situation.
My two bobs worth..