As the name says to do this karma loss is pretty much unavoidable, but you dont lose that much.

Find the Outcast base Fort Independence. Once there agree to helping them get supplies (talk to morgan first then the leader).

Once you're allowed to trade with them go find the Alien Blaster. Pick-up all the ammo for it as it is what we need for the trick.

Go back to the outcasts and sell that guy the ammo. Pick stimpacks because it gives you 11 stimpacks for 12 alien ammo.

Once you run out of ammo to sell steal it back but watch out if he catches you because you'll have to do it all over.

Steal it back and sell it again as your heart desires. And if your a good character like me I'll warn you again - you will lose karma when you steal the ammo!

I got 409 stimpacks in 5 minutes.