echo same menu items across multi-site platform

I am trying to echo main theme's menu items across the headers of other sites in a WP multi-site environment and was wondering what is the proper way of doing this. I tried iframe which works but there is a delay in displaying the header. So, the body gets loaded and couple of seconds later the header populates. Here is the iframe code I have:

<iframe class="header-iframe" src="http://ift.tt/1GER9rO" frameborder="0" scrolling="no" width="100%" height="233px;" ></iframe>

(please excuse my way of questioning)

I notice that in one of the site's header, to echo something, it show something like this:

<?php bloginfo('siteurl')

now, if I want to display from the main theme, what should be my PHP statement? Thanks for all help.