Honestly about the only gimmick to speak of is the sheer speed you have to do it in. The super cancel essentially comes right after the the hit connects, so you basically have to start the input right after you put in the input for the rekka. After you figure out the timing on regular rekkas, try spacing yourself so the first hit of the rekka whiffs and trying to get the super there. Once you figure it, you should be able to get the trial.