From the help file:
- /pop <delay> [#channel] <nickname>
Performs a delayed op on a nickname. The purpose of this command is to prevent a channel window filling up with op mode changes whenever several users have the same nickname in their auto-op section.
mIRC will pause around <delay> seconds before performing the op. If <delay> is zero, it does an immediate op. Before performing the op it checks if the user is already opped. If you do not specify the #channel, the current channel is assumed.
This command is exactly what you needed. In your "on join" scripts you can use these commands (each on different computer):
- pop 2 # $nick
pop 6 # $nick
pop 10 # $nick
Good luck