How do I pass $in_foooter to wp_enqueue_script() without passing other params?

Try passing array() for $deps, and NULL for $ver:

wp_enqueue_script( $handle, $src, array(), NULL, $in_footer);

Or, using your function call:

wp_enqueue_script("myscript" , get_template_directory_uri()."/js/myscript.js", array(), NULL, true );

By the way, passing the script itself as a dependency to itself will probably make something blow up.

Note also: if your script depends on jQuery, just pass jQuery as a dependency, instead of enqueueing it separately:

wp_enqueue_script("myscript" , get_template_directory_uri()."/js/myscript.js", array( 'jquery' ), NULL, true );