Trent and Chris both make excellent points. I love playing high notes, the big thing is practice. The more familiar you are with the fingerings and voicing of the notes, the easier they become. The using of standard fingerings is important, in the beginning, but sometimes you need to change a fingering for a high note because of the proceeding note and if it is slurred or tongued. I am working on a concerto now that I use 3 or 4 different fingerings for high e. Sometimes changing the original fingering IS better for the situation or you.
Focused air stream really helps, like blowing through a coffee straw, also feeling the response of the reed on your teeth, through your lips, without biting. ( that sounds like scratching your head with your left foot).
Avoid making your reed tubes too small, that actually seems to kill the high range for me. A firmer reed helps (heavier at the back of the blade), as long as it doesn't wreck finesse and supple control. Reed shape can help, I use the Thunemann shape for French concertos and works with a dominant high register. Rieger made me an excellent version of my old Walt shape that I use for regular stuff in the orchestra and a second (Walt2), wider version for Buffet French bassoon reeds and full bodied German reeds.
I actually play, lips pretty close to, even touching the wire, which I think also helps with high range, many of those high harmonics are close to the first wire. (I have also found that extreme highs start to creep toward the middle of the reed, but nobody ever writes for those notes. I actually found a lot of those fingerings and posted them on YouTube under bassoon high notes, http://youtu.be/DudNC-nkr7Y).
Bocals can also help, I only use my Allgood if I can switch away from it, I have to change too many fingerings for intonation to use it very often, although it is also great for very loud playing and I can use it to play up to the C (C6), an octave above the Rite without my teeth. Some Fox Bocals work well for high notes. I am actually quite happy with my silver plated Wolf Grundmann bocal. It is not quite as supple as my Heckel c1 but it easily makes up for it with its finesse in the high range. I can pop out a high Bb5 with the Grundmann. I think Trent might be able to help with Bocals. I never found the bocal hole near the reed helped more than a high bocal or good reed. I think that's because most of the Bocals I've tried with the hole were either bad or bad for high notes in the first place.
Some bassoons are terrible for high notes. I love my horn, never want to change it, but high notes are not one of its fortes. I have a much better high range on practically everybody else's horn. If that's the case there is still a way, there are so many variables.
A low tech trick is to drill a hole between the first and second wire on the reed. I heard about it from David Wells and I think Bernard Garfield used to do it. It loses too much air for me, but I might have have made the hole too big. I never took the time to try different drill bit sizes to see what was the smallest size that wouldn't hiss badly but work for highs. I would guess something smaller than a bocal button hole. I would only use it for notes above G5 anyway.
I'm sure I am forgetting something, practice and familiarity are key and having fun with it can motivate you to do more. My high note journey started when I was a high school kid having to play Shostakovich 8, it was a long and difficult week, the concert went well, but I never wanted to stress like that over high notes again.
Best of luck!!!!
Principal bassoonist, Orquesta Sinfonica de Galicia, A Coruña, Spain. Bassoonist, bassoon dad, bassoon husband, bassoon uncle, bassoon brother and bassoon son.