Add cross selling to multiple products at once?

Is there any way to create cross selling relationships for multiple products at once? Or perhaps to create cross selling relationships for categories instead of products?

For example, if customer adds any of these selected products, then show this other list of products on the view cart page.

Or, if customer adds any products from this category, then show this list of products on the view cart page.

For the purpose of explanation, I'll refer to the products as the primary product and related products.

I've been able to add multiple related products at a time for one primary product, but I am unable to add multiple primary products along with multiple related products.

*edited to use common terminology*

Edited by Brett - 13-March-2013 at 7:27pm

I feel like I'm only asking for one thing. The current workflow for adding cross selling relationships is like this:

Marketing > Cross Selling > Add new relationship
Step 1: Select ONE product. This is the primary product. The "trigger" product where if you view this product, other products will be shown.

Step 2: Select a list of other products. You can select as many as you want, and all of these products will be shown on the page of the "trigger" product.

What I want is to be able to select multiple trigger products at once. So basically, I want to see check boxes on this (http://imgur.com/O3QKJEY) page, instead of radio buttons.

I want to be able to select a list of products, and if the customer adds any of those products to the cart, then I want to show a handful of cross selling products on the view cart page.

Disregard the category thing, as that is asking for two things at once and I should probably focus on one thing at a time.

Is what I'm asking for possible with the default installation, or will I need to custom code it or buy your plugin?