Make a SCAIP block that inserts an arbitrary sidebar in the post, with alignment properties. When this block is used, prevent the automatic ad inserter from running.
Make a settings-page option that, for new Gutenberg posts, automatically includes the preset number of ad-unit items on the page, with the correct sidebars for "sidebar 1", "sidebar 2", "sidebar 3" etc chosen in the inserted blocks.
Some ideas: