List Management API Limitations?

I've been spending some time trying to digest the api documentation, but have run into a stumbling

block.

There is one particular List Management API (addlistsubscribersinbulk) that, using Postman, I have successfully posted a new user email to the list of, but I need to include a variety of custom fields as well (first name, last name, company, phone, etc). I've also seen that you have a custom/add function but not any way to post to those new fields. Is there some amalgamation of the two that enables me to programmatically post a variety of details to a selected contact list?