Once Round, The Hacking Way
Assuming that you only need the train to take the path once, that it doesn't loop, then there's a hacky way to do it. The first thing to do is to read the second half of this post and digest it
http://www.celephais.net/board/view_thread.php?id=37116&start=36&end=36
It might be worth making a quick test map and see if you can make a train that switches from one simple loop to a second simple loop first, to make sure you understand the hack.
Once you've got that down, the next step is how to do the specific thing you want. The trick here is to stack two path corners on top of each other at each stop, and make them target each other. While your train is "waiting" to be triggered at a "stop", it's actually going to be going back and forth between these two points, just moving nowhere because they're at the same location.
When you want the train to continue on, you remove one of these two stacked points using the trick in the linked post("use s_explode6"). Then you have another path_corner with the same name later in the entity list, and it'll head to that. You might find you have problems if you want it to stop and wait at that next point, you will need to make sure it's the other path_corner stacked at that point which has "use s_explode" set, or both will get removed when you target the first one to be killed.
The main problem I can see arising with this hack is the sound, you'll constantly hear the platform starting to move while it's "stopped", so you might need to make it a silent platform. If this is a problem, or you want the platform to loop endlessly but still wait for a trigger at each point, then you'll need to go the QC way. Which isn't too bad, this is quite a hacky hack.