You could disable the visual stims emitted by those AIs, in the same script that kills / knocks them out.
$name_of_ai.StimEnable(14, 0);
14 is the ID# of visual stims (found in script/tdm_stim_response.script), 0 is to disable.
(If they start ragdolled at map start you can just disable the visual stim in the S/R Editor).
One method is to encase him in a brush of nodrawsolid and apply health 1000. If you want to go further you could make a looping script that refreshes his health every few seconds.
For never becoming alert, you can set all his acuities to 0.