You can’t, I’m afraid. There is no plausible way within the gameworld that a helot has that negotiation with Calea – no basis for the strained family trust that underpins the aristo-Calea bargain, or any measure of trust at all.
There are other gameplay aspects that only a helot gets, notably the return of Carles the jongler; and as we’ve discussed above, in future games male helot characters may have a Calea romance that no other type of character gets.
While I’m crushing hopes and dreams: I’m not planning Cerlota as a playersexual or genderflipping character. Female MCs may be in luck (though with more difficulty if you’re a Theurge yourself); male MCs will have to be satisfied with a Platonic relationship.