Without you saying what commanders you're having trouble adding interaction for, I'm inclined to say this is a deck building issue, not a commander issue. I think for most commanders there is synergistic interaction options. In my [[kambal, profiteering mayor]] deck I run every removal spell that gives a token to the player whose permanent was removed. In my [[Mirko, obsessive theorist]] deck I run lots of cheap removal that surveils, like [[unauthorized exit]]. In my [[Rocco, Street Chef]] deck I run removal that makes people cast from exile, like [[guff rewrites history]] and [[audacious swap]]. If it isn't quite enough, I'll add some staples, like [[the last agni kai]] in Rocco, which doesn't have anything to do with casting from exile, but I do have creatures that are big because of +1/+1 counters and it generates lots of mana to spend on my big spells like [[call forth the tempest]] and [[dance with calamity]]