Just found out that Q171424 describes what I want to do. Now I just have to find the best way to limit it to running once.

; This file called Del-Reg.INF deletes the registry entries listed
; under the [RegChange] section. In this example it deletes the
; UserName value name under the key HKLM\network\Logon

[Version]
signature="$CHICAGO$"

[DefaultInstall]
; DelReg = RegChange

[RunIt]
DelReg=RegChange

[RegChange]
HKLM,Network\Logon,username
HKLM,Network\Logon\keyname,