Calling Links using Custom Fields

I am trying to achieve a specific thing using WordPress and can’t seem to find the right answer / look for the right question at the mo.

The desired outcome is that I can insert specific links from the link manager, into specific pages using the custom field functions.

So far I have managed to : Check the custom field for a value, assign the value to a string and perform a successful IF routine thingy in the right place. The difference this time is that I want to return the variable INSIDE the WordPress arguments of wp_list_bookmarks.

I have tried using something like this:

<?php get_bookmarks('include=$related_links'); ?>

and
<?php get_bookmarks('include=' . $related_links); ?>
to be used in a similar manner to

<?php get_bookmarks('include=1,2,3'); ?>
but while the IF statement shows other parts (telling me that it sees the custom field) it doesn’t return any HTML, links or otherwise.