Custom queryFn reusing other endpoints

Using code from https://redux-toolkit.js.org/rtk-query/usage/customizing-queries#performing-multiple-requests-with-a-single-query

Note that I added the endpoint getRandomUser:

import {
  createApi,
  fetchBaseQuery,
  FetchBaseQueryError,
} from '@reduxjs/toolkit/query'
import { Post, User } from './types'

const api = createApi({
  baseQuery: fetchBaseQuery({ baseUrl: '/ ' }),
  endpoints: (build) => ({
    getRandomUser: builder.query<User, void>({
      query: () => ({
        url: `users/random`,
      }),
    }),
    getRandomUserPosts: build.query<Post, void>({
      async queryFn(_arg, _queryApi, _extraOptions, fetchWithBQ) {
        // get a random user
        const randomResult = await fetchWithBQ('users/random')  // avoid repetition
        if (randomResult.error) throw randomResult.error
        const user = randomResult.data as User
        const result = await fetchWithBQ(`user/${user.id}/posts`)
        return result.data
          ? { data: result.data as Post }
          : { error: result.error as FetchBaseQueryError }
      },
    }),
  }),
})

Since in my example code I already have a getRandomUser endpoint defined, I would like to avoid repetition in getRandomUserPosts await fetchWithBQ('users/random') and directly call the endpoint getRandomUser.

I tried to access it with _queryApi.endpoints but it doesn't seem to be defined (I don't know if it can point to a key in the very same object endpoints) and even if it would I didn't know how to use it to replace the repetition.

How to approach these situations?