Check the forum archives, this has come up before, and besides the video (so THAT's who's responsible for a lot of this wretched bobber affliction suffered by many a poor Bullet) someone posted some very helpful pictures two or three years ago showing how they had done it by modifying the existing parts.
Apart from buying our hosts' conversion kit (which someone ought to plug as this is their forum!) you could also take the complete box up to Henry Price in Rockhampton, he will modify it for you.
Indeed the conversion kit is available from our hosts IMHO you should go for it.
The 5 speed box will transform your bike, plus you can probably sell your old box to recoup some of the costs - that's what I did when I converted the 612.
Oddly enough when I was out riding on it a few days back I was thinking how much more enjoyable the ride is to be able to change gear easily / positively, but even better being able to find neutral in traffic, it really does transform the whole riding experience and if you do it you will be asking yourself why did I not do it years ago.