OK, a question of limited practicality, granted, but...
The Cortex Bombs are listed with no Essence but a bracketed Capacity rating (capacity consumed). Given the text that discusses installing in cyberlimbs, I assume the capacity rating is "when installed in a cyberlimb."
What if you install it in someone's, you know, cortex? Would that be a "zero-essence/zero-capacity install"? I assume it doesn't require a Cyberskull or Cybereye or Cyberear just in order to have some capacity in your head to install the bomb into?
It seems odd that installing something as large as a Frag grenade into your skull wouldn't affect Essence, but I guess if it comes to that, you're probably past counting.