widget loop: collect queried posts IDs in array to exclude these in main loop

I am currently building a magazine theme and need a little help handling multiple loops. I need to somehow collect the queried posts post_IDs in the widget code in order to exclude these posts from the main loop.

So on the front page (= blog page) the theme displays the following:

• WIDGET 1: 3 featured posts (posts from category 123)
• WIDGET 2: the 5 latest posts from category XY
• WIDGET 2: the 5 latest posts from category ABC
• the main loop

Each post can have more than one category.
The main loop is supposed to exclude those posts that already have been queried by WIDGET 1 and WIDGET 2.

So in the WP Codex there is a paragraph about how to do this with multiple loops. The solution looks like this:

For the custom loop

<?php $my_query = new WP_Query( 'category_name=featured&posts_per_page=2' );
while ( $my_query->have_posts() ) : $my_query->the_post();
$do_not_duplicate[] = $post->ID; ?>

For the main loop:

<?php if ( have_posts() ) : while ( have_posts() ) : the_post();
if ( in_array( $post->ID, $do_not_duplicate ) ) continue; ?>

**Idea**
As you can see, I use the same widget more than once. This makes me think I can’t just go and use $do_not_duplicate[] = $post->ID; in my widget code because it’ll get overwritten, won’t it?

How can I store the IDs of the posts that have already been queried by the widgets in a variable or an array to use them in my index.php file ?

I’m glad if anyone could give his/her thoughts on this.