Requires a Dummy account
Open the command console: ESC > Gear Icon > Under the keyboard tab select Advanced > Check off Enable Developer Console
Press the ` button to open the console and type:
map ctf_2fort; hostname "boost"; sv_lan 0; sv_cheats 0; (I had to input this twice to be detected on my LAN for some reason)
That will create your match. Choose Demoman on the Red Team. Then type the following command:
mp_teams_unbalance_limit 0; mp_idledealmethod 0; mp_idlemaxtime 0;
Then the command:
sv_cheats 1; sv_gravity 1; sv_cheats 0;
Go somewhere with a roof. Launch an enemy into the air using an explosive and finish them off in the air. Because we set the Gravity to the lowest amount without turning it off completely, the enemy will be in the air for a while. Default Gravity is at 800 to set it back to normal