Loading large KML layers without blocking UI

Question

I'm loading large KML layers using the google maps API and geoxml3, via parseKMLString.

Relevant question and Example using this function.

While these files are being rendered to the map, the UI is frozen. As this is using google maps, I can't put this code in a Worker and wrapping this in a promise isn't going to change anything.

Relevant code block:

 var latLong = new google.maps.LatLng(37.0902, -95.7129);
 var myOptions = {
           center: latLong,
           zoom: 10
 };
 myMap = new google.maps.Map(document.getElementById('map-canvas'), myOptions);
 geoXmlParser = new geoXML3.parser({
           map: myMap ,
           singleInfoWindow: true
 });
 geoXmlParser.parseKmlString("long-kml-string", geoXmlParser.docs); 

I'm also open to alternatives to both loading these files and other libraries that may exist to assist.