Can be boosted solo with a bot.
Go to "Practice with Bots", select the Deathmatch mode, and pick any map you like. I suggest settings the bots to easy.
When the game has started, kick all bots from the game with the console: bot_kick
Then, have a single bot join the enemy team: bot_add_t or bot_add_ct
Have the bot kill you 4 times, and on the kill screen it should say that he is dominating you. Then kill the bot.
Repeat as necessary.