How Do I?

[KWonline]

I did a search already and couldn't find anything that answered my question.
I live in the Uk (so no coppa laws for me) and run a forum which could attract members under 12.
I do not want to restrict their posting or access to forums or anything like that.
What I do want is to disable certain profile fields (Instant Messaging Addresses) when they signup.
I'd be grateful if anyone could tell me how. Or whether I would need to request a hack for this.
Many Thanks.