Alright so basically what your gonna wanna do is your gonna wanna get a outpost NPC or involuntary player or player team NPC.
For the outpost NPC just get them knocked out, use flash grenades, stun sticks, etc, etc, just do whatever it takes to get someone knocked out without damaging your reputation too badly.
oh yeah also they need to be alive and generally unharmed

ok so you have your evil devious weapon of knocking people out or on the ground, nice.
just uh go up to the involuntary victim, inject them, stun them, etc.
and shove handcuffs on that bad boy.
Security guards are most of the time preferred because you can just use their handcuffs.
Also flashbangs are the best for this because even if you miss you still have enough time to splash those handcuffs on.

now what you wanna do next is you wanna go get a divers suit, make sure to remove the oxygen tank or have an empty one in the suit
this shouldn't be very hard to do unless your captain sold all of your suits.
diving masks don't work unless you put welder fuel in it, but thats too "expensive" and it takes resources. and it's just easier to use a diving suit without a tank

So you got the suit, you got the handcuffs, now all you need to do is slap it on that bad boy and watch this bozo die.
When you do this step, make sure to have the guy wanting to level up medical close-by.

Alright now heres the finale ladies and gentlemen, I call it, aggressively beating them until they heal.
In the health menu, when they pass out press CPR. wait until they get revived, then they pass out, and press CPR. Then just repeat the steps.
Theres a slight chance they might go braindead and never wake up if you wound them too much from messing up CPR, one time I had a guy die on me just because of the bruises he got by my 96 medic.

Also, sometimes the guy trying to level up is so bad at CPR that they barely ever get XP from it, so just always use your ship's medic.

You could just use a useless player or assistant but its way easier to use a outpost NPC you don't have to spend resources on when the round ends. When you decide your done with them you can either A, let them suffocate and then drag their body to your sub and take their stuff, or B, knife them for weapon XP, drag them to your sub, and lose rep and take their stuff.