I'm no coder or anything, but I was able to do this by going into the Bot_Blockhead zip, opening bot_base.cs file, and scrolling down until you see bot spawn options. From there, you can set it so that the bot will not spawn unless within a certain distance from a player. You can even set the range. BUT, of you don't wanna do that, you can use the base events in the game.
OnBotSpawn - Self (Not Bot!)- setBotType - None
This will make it so that the bot won't even spawn. You could then make event triggers to do so.
OnPlayerTouch - (named brick of bot) - setBotType - (whatever type of Bot you want it to spawn as)
You can even make it so that the bot won't spawn after you kill it.
OnBotDeath - Self - setBotType - None
It takes a bit more work, but I think I was able to make the beginning of a Serious Sam Map like this, and it worked great! But I do remember that I had to set the tick time for some events to 500 otherwise they wouldn't trigger.
Hope this helps, fellow Bot loving brother!