You can do it legit, but it will be much easier with a boosting partner. You must have at least 20,000 points total to upgrade all of the units in one match. Each unit takes a total of 5,000 (Level 2 - 2,000, Level 3 - 3,000). Kills give you points for damage but it may be easier to exchange taking over control points. You receive 125 pts for each control point you fully neutralize by yourself (make dark) and 250 for each control point you take control of by yourself (make your color). Host a Multiplayer Versus Ranked game and set it for 2 players and "No Limit" for the Round Duration and a map you and your friend agree on so your friend can find your game. If you wish you can set the match to Conquest so at the end you can take over all the control points and receive the "Hydropwnage" achievement as well.