Delay when using WebGLInput.captureAllKeyboardInput = false;

I'm trying to turn off keyboard input to a WebGL player, but I notice that there is a small delay before I can use the textbox on the website. I assume this is because the player defaults to capturing input until it's turned off by my script (in the default script execution order).

 void Start()
 {
 #if !UNITY_EDITOR && UNITY_WEBGL
         WebGLInput.captureAllKeyboardInput = false;
 #endif
 }

Is there a way to turn off keyboard input as the player is loading? Can I put the above code in a better location? Or will increasing the script execution priority of the script help?