Apparently, this feature was done away with since IP.Board v3.3
IPS's rationale is related to the way they form links to pages and posts: if you allow members to have different settings then one person's page two is another's page ten (for example). If one of those members tries to send a link to another member with a different setting by copying the link in their address bar, it won't work, and I have certainly gotten complaints about this issue in the past. There really isn't a clean way to deal with this problem except to do what Invision did, and remove the feature entirely.
^ From the IPS community forums.