Select image sizes for srcset

Hi rsmith4321

Sorry for the late reply. Yes this is possible.
The following information is based on the 3.0.0 version of the plugin that we just released and it will also work in WordPress 4.4 where responsive images will be integrated.
You can use the wp_calculate_image_srcset filter to remove an image from the array that is used to create the srcset.

add_filter( 'wp_calculate_image_srcset', 'my_callback_function' );

function my_callback_function( $sources ) {
    unset( $sources[100] );
    return $sources;
}

I hope this helps!