The trick is to use a brake segment of track just before a transport segment. If you open up the settings on the brake segment, you'll see the option for "Complete Stop" and "Transport Device". You want both of those checked. Then also check the "Launch" box and you should be good to go.
So once you've got the brake segment (should be about the length of the train - at least, that's how I do it), you then just add the transport segment and continue doing launches as you did before (the train enters the transport segment moving, so it's just the same as a rolling launch).
Obviously you'll have to play with the settings to get the launch effect you're after, but that's how you make the train stop before a launch.