OK, so after a tiring spree of choosing all the available options I finally give up on this achievement. Here is what I have done so far.
At the warehouse, when you take a moment to consider your options and choose to kill everybody and take all the wealth for yourself, you get your first skill check, which is based on Guts. 14 Guts is enough to pass, haven’t tried a lower amount.
If you pass this, there is another skill check which is based on Leadership to persuade the captain to drop his guard and kill him. 12 Leadership is enough to pass this, haven’t tried a lower amount.
If you pass this as well, there is a third (and probably the final) check when trying to get away with the treasure which says “you are not commanding enough, bummer”. I am guessing this is also based on Leadership, but unfortunately 12 is not enough. You get killed right away.
The trick is to choose the options in the marine school so that you will have enough Guts and Leadership skills when you graduate. After the graduation, it is not possible, as far as I have seen, to increase either of these unless advancing the main storyline and possibly eliminate the “get away with wealth” path.
The problem is, during the training phase if you choose the right options you either get 12 Guts - 13 Leadership or 14 Guts - 12 Leadership in the end. Both are insufficient to pass all three checks I wrote above. I have not been able to find a way to increase Leadership to 13 while keeping Guts at least 13. I have exhausted possibly every combination (with the guts enhancing implant obviously) but I can’t get 13 Guts and 13 Leadership no matter what I do.
There is no walkthrough anywhere on the internet and I have wasted too much time already on this, so if anybody can give an insight to this, it’d be nice.