profile fields only visable to like group members

[jwhale]

Can anyone tell me how to acheive the following simple hack.

I have added some user profile fields and I only want them visable to people that are members of the same group. In simple terms, group "a" members can see the custom fields of another member in group "a", but not of a member in any other group. The custom feilds are not visable or searchable in the members list, only visable in the usercp.

any help appreciated

thanks