How does one cheat???

[therother]

Disinheriented is the first level of the Exheir trait line.

So try:

give_trait "Gaius Scipio" Exheir 0

Either that or modify this trigger from RTW/data/export_descr_character_traits.txt:

;------------------------------------------
Trigger disinherited
    WhenToTest CeasedFactionHeir

    Condition not Trait Exheir = 1
          and not IsFactionLeader

    Affects Exheir  1  Chance  100

Edit: Actually, I should say that I've not tried the above modification, so perhaps it either won't work or will have nasty side-effects. Anyone brave enough to try it?