It is surprising to me that a trigona that size would not be more branchy, like Bob's. There are other Euphorbias approximately like the plant which might be a better fit. Regardless, all the above advice sounds quite reasonable to me... beheading the plant, moving it outside. The simple act of beheading should trigger branching, which is not going to work out well if you do it too high up on the plant (sort of an inverted pendulum going on there).
I have started trigonas from segments without an intact growth point and it works out just fine. So if you want to start 5 plants, go for it. Just be sure to keep the up side up.
Be careful not to rush the plant into lots of sun if it's been indoors with filtered light. This time of year direct sun is about maximum strength and that can be lethal to plants which have spent a long time in a sheltered position. So maybe over the course of a few weeks find a way to gradually increase the exposure. The problem outside is the wind will wreak havoc on a stem that long if it is not securely staked or somehow otherwise fixed in place.
These plants tend to enjoy a lot of exposure and if you want yours to grow compact and full from here on out, you will probably have better luck if the plant gets hours of daily sun (indoors through a window). Don't know what the situation is at the moment.
