unless you can get a DLL to get the ping from ingame, i don't recommend it.
IRC ping can be much different to game ping, so you could be kicking someone with low ping but high irc lag.
Anyway, the only way is to ctcp ping everyone set your $ctime to a variable, then when ping reply comes in, minus ur current $ctime from that in the variable.
However, some people might not respond to ctcp ping, then you are stuck because you cannot find their ping from irc.