How to add companies to Company Based List without filters?

@KJonsson, I found a much cleaner solution. Simply create a Static List and choose really any filter (you’ll delete it in a minute, so try adding one you know doesn’t have a ton of results). Once the list has populated all your results, you can select all companies and remove them from the list. Since it was a Static List, the companies will not be re-added, and you are now free to manually add companies to the list.
Now just go to your Companies object, manually search for the company you want, select the option “Add to static list”, and select the list. Done!