for what it's worth, some things to consider....
there's no way, based on the information provided, that anyone can effectively help this guy huck this jump. we don't know the track conditions, what the jump face looks like, what the landing looks like, or what kind of rider he is...or, for that matter, what kind of riders the ones who do clear it are.
there are just too many variables. how far out of a turn is the launch? how much taller is the landing than the takeoff? soft dirt or hard? bumpy run up or smooth? into the wind?
having said that, seat bouncing might help - length and size of a jump don't dictate whether you should do it or not. it's launch angle and ramp height relative to approach speed. the faster you're going, the shallower,and or taller it better be, or you'll end up on your head. in other words, right out of a corner...short and steep is ok. on the other hand, seat bouncing the stepup at cooperland (dirtweek), is ok, because it's steep, but tall, so even though it's a hi-speed approach you don't get bucked off. it all depends....
why? because timing IS important. seat bouncing isn't smashing the bike into the jump face, then letting the shock rebound toss you like a pogo stick. that's the path to a broken wrist. seat bouncing works because you've effectively attached your center of mass more directly to the center of mass of the bike. there's no bendable element (your legs) between you and it, so you get deeper compression, and therefore more stored energy. the timing part comes in when you release that energy and UNweight by standing up at the moment the front wheel takes off. you use the now relatively rigid platform of the footpegs as a point for starting a vertical leap with your legs. as you propel your body skyward, your upward momentum, combined with the now crazy fast upward momentum of the bike, gives you a taller trajectory. the takeoff angle also factors in. look at any pic of a pro right as his front wheel leaves the lip during a seat bounce. there's usually a little wheely going on. it all works together to get you more lift.
if your timing isn't good enough to do all that in 4th gear, don't try it on that particular jump face. just do the intermediate method of compressing into the face while standing, then unweighting on takeoff. the effect isn't as pronounced, but it's much safer.
wp.