Use an API Call to Populate Custom Data Connector Settings

I've created a custom connector I've imported into Power BI Desktop. I'm using it to pull in a very large data set, which is too big to pull in completely in a single request. So I want to allow a user to select a certain subset of the data in the connection info (DataSource.Contents) screen. To do this I have a few dropdown menus that allows them to select a subset. These dropdowns are pretty dynamic. Right now if I hardcode my dropdown list in a function and return it in a function it works:

dropdownList = {
[id=""123, "name="example dropdown"],
[id=""124, "name="another example dropdown"]
}

But I want that function call to return the result of an API call to dynamically load this list. I am using the following code which I know works during the actual data retrieval for the custom connector:

content = Web.Contents("https://my-api.com/unprotected/endpoint/returning-json", 
            [
                Headers=[
                    #"Method"="GET",
                    #"Content-Type" = "application/json"
                ]
            ]
        )

This code works when I make it run in the Contents section of my DataSource. Is it possible to get this to run during the data connection settings screen? Is there some async/await type keyword I am missing?

And if not, does anyone know of another way to allow a user to define the parameters of the content they need so I can make an API call for the data on a large dataset that will not time out?