Help with pulling custom userfield data

[Mark.B]

Ok, I like to work things out for myself but I'm stuck!

I have created a custom profile field to enable users to set a "display name" which, in certain locations, replaces their normal username. (We switch this on for weekends at a time for a bit of fun).

Over the months I have gradually hacked about with both plugins and php files, modifying queries and templates so that the custom field shows up in various places if the user has one set.

Now, I know how to structure the queries etc, no issues there.

Currently I have it working in the following places:

Posts
Getdaily/Getnew
Member list
Who's Online (forumhome)
Who's Visited (Paul M hack)
Who's Posted (Paul M hack)

This covers most of the places I really want it to work.

However, the one bit I cannot fathom, is the lastpostinfo section of the forumbits on forum home.

I know the variable I need to play with is $lastpostinfo[lastposter], but for the life of me I cannot work out where the query is that sets this variable, so that I can add in the custom profile field.

Anyone got any ideas?