Adding to the ReputationFrame scrolllist is going to be tricky because you don't control the data.
To add one to you own frame then the actual list entries use the ReputationBarTemplate (this will place a rep entry at the top of your screen)
Lua Code:
local f = CreateFrame("Button", "nkttennesseeRep", UIParent, "ReputationBarTemplate")
f:SetSize(200, 50)
f:SetPoint("TOP")
f.Container:SetAllPoints()
f.Container.Name:SetText("The Nkttennessee")
f.Container.ReputationBar:SetStatusBarColor(0, 1, 0)
f.Container.ReputationBar:SetValue(0.5)
f.Container.ReputationBar.BonusIcon:Hide()
f.Container.ReputationBar.FactionStanding:SetText("Awesome")
f.Container.ExpandOrCollapseButton:Hide()
f.Container.Paragon:Hide()