Inherit the model:

``` python
from odoo import models

class MyModel(models.model)
    _name = 'my.model'
    _inherit = ['sql.request.mixin']

    _sql_request_groups_relation = 'my_model_groups_rel'

    _sql_request_users_relation = 'my_model_users_rel'
```

See implementations in the modules `bi_sql_editor` and `sql_export`.
(same OCA/reporting-engine repository)