I have a selection field as follows:

source = fields.Selection([
('one', 'First'),
('two', 'Second'),
('three', 'Third'),
('four', 'Fourth'),
('five', 'Fifth'),
], required=True, default='one')

How can I show but inactive some of these options?

at the moment these options are all visible and selectable but I want some to be visible but inactive so not being selectable.