Create a Private Match of Rescue on either Beach or Underground.
Invite your boosting partner. Now it doesn't matter which faction you choose seeing as how you'll take turns switching between rounds anyway.
Set the Match Options to the max, the ideal set up would be 20 minutes, Best of 3(doesn't really matter), You can leave the "Medkits to retrieve" at 5, but change the "Survivors to Kill" to 100.
Start the game.
Player 1 (The Solarii) : From your spawn point, Head to the Survivor's side of the map and stay in close vicinity of the Drop Zone for the medkit (shown as a medium sized blue circle on the floor).
Player 2 (The Survivor) : Once you spawn, haul ass straight to the first medkit, now make your way back with it, stopping RIGHT next to the Drop Zone (NOT delivering it).
Player 1 now shoots and downs (preferably w/ a Headshot for more points) Player 2 AND finishes him/her off w/ , getting even more XP for the Execution. The first kill should grant you about 2000-3000 XP.. There's an ammo box in the same room (on both maps) as the Drop Zone if needed.
Player 2 runs back after spawning then picks up the medkit (quickly before it disappears and spawns somewhere else) to die again and so on and so forth.
Simply rinse and repeat. That's it.