Those aiming for wealth, status, and influence know that writing as a skill doesn't pay off, not in the ways they want. Even if they are adept writers, they tend to resent whatever time they have to invest in writing. That's where you come in, if you have above-average writing skills and can identify and mirror their tone, mode of organization, and word choices. Yes, you become their informal ghostwriter.
As their time is freed up to do other things and as their written products are praised, they will view you in a positive way. They won't want to lose your ability to ghostwrite for them but they will probably open up additional opportunities for you. If they rise in the organization, get a plum job elsewhere, or open a business, they are bound to ask you if you want to come along.
How to start the ball rolling on becoming someone's un-designated ghostwriter? Observe that they are struggling and offer to pitch in and help. Do the task well and quickly. Repeat that a few times. Human beings have a quick eye for shortcuts and you are providing a quality one.