Can be done w/ variable and bot events events:
OnBotKilled>NamedBrick>Wave2Spawns>VCE_ModVariable> [Kills] [Add] [1]
OnBotKilled>NamedBrick>Wave2Spawns>VCE_IfVariable> [Kills] [=] [# Of kills till wave 2]
VariableTrue>NamedBrick>Wave2Spawns>SetVeichle>Zombie