python - Declare model before create connection in ming

Question

I want delcare my models before make connection with database (for some reason like multi-threading, and dynamic load of database config uri).

Documentation say to use like that:

from ming import create_datastore
from ming.odm import ThreadLocalODMSession
from ming import schema
from ming.odm import FieldProperty
from ming.odm.declarative import MappedClass

session = ThreadLocalODMSession(
    bind=create_datastore('odm_welcome')
)

class WikiPage(MappedClass):
    class __mongometa__:
        session = session
        name = 'wiki_page'

    _id = FieldProperty(schema.ObjectId)
    title = FieldProperty(schema.String(required=True))
    text = FieldProperty(schema.String(if_missing=''))

We can see what model declaration need session (in __mongometa__). How can i declare WikiPage model without session variable ? And set it later ?