Using profile field in forum display

[RustedBucket]

Here's what I'm wanting to do and I realize this might require core modifications possibly.

Currently running: VB 3.5 Stable

I have usernames that are generic numbers (ie: R55555). That number corresponds to an employee name. I'm currently storing the users Real Name in a profile field (ie: field5). This obviously works fine in the post bit, but I also want to display the real name in the Last Post information. So on all the forum views, the Last Post By is not the username but actually the profile field. My problem is, figuring out where to do this. Is it a code mod or is there another method that can be used in the new system?

Thanks