Changing view modes/disabling MIE on a per-block basis

Problem/Motivation

We are using the Menu Item Extras module to field menu item entities for the main nav menu in order to create a megamenu. It was all going well until we realized that there was no means via the UI to customize the view mode on a per-block level. So our footer and sidebar menu blocks (which also use the main nav menu) are displaying all mega menu content. I've looked around in the preprocess hooks and haven't found the silver bullet there either.

We're at budget on this project. I'm hoping there's a means for rendering the secondary displays of the main nav as simple menus without having to get into a whole bunch of custom templating. Attaching screenshot of how the footer/sidebar main nav blocks appeared before and after the Menu Items Extras implementation.