Firstly, thanks for using my library. It's worth noting that the library is merely a way to simplify the generation of the Google Maps code. It constructs the JavaScript and HTML on your behalf making it quick and easy to add maps to your page.
There are a million and one ways that a developer might want to interact with the Google Maps API and it's impossible for the library to cater for every single instance. As a result, there are times where, in a bespoke situation like this, you may need to add your own code so it performs as you require.
As a result, might I suggest you simply add in the custom JS you require after you do echo $map['js']. There is a function available that comes with the library called createMarker() which, if you view the source code, you will see.
In pseudocode this will look like so:
<?php echo $map['js']; ?> <script type="text/javascript"> // Get marker(s) with ajax // Call createMarker() function to add marker(s) to map </script>
I hope that helps somewhat.