dont do a full entry on the rail as you would usually do . keep your shoulders looking down the rail, which will give some momentum for the switch up.
when you do a front side 270 out , your upper body rotates before your lower body. thats the same kind of motion you want to do but a the begining of the rail.
look at some footy of guys doing 270 outs and frnt side swtich ups, dont look a wallish or top pros cause their been doing it for year and they dont have the same motion and thescnique blablabla for you guys to learn this trick. look at some kid who just got the trick and is really exagerating the technique and movement for this trick.