At the API level, Custodial Accounts work the following way:
Synapse-US
View API
import os
from synapse_pay_rest import Client
from synapse_pay_rest import User
from synapse_pay_rest.models.nodes import SynapseUsNode
kwargs = {
'nickname': 'Custodial Account'
}
node = SynapseUsNode.create(user, **kwargs)