Regarding:what would be the alternative

Override the default_get Like:

def default_get(self,cr,uid,fields,context):
		res=super(multi_package_shipment_wizard,self).default_get(cr,uid,fields,context)
                #Now update the res here.

In ODOO Admin can also set the default value of fields from   Setting->Technical->Actions->User defined Defaults .
For example for setting default account_id in account.invoice :

1. Go to Setting->Technical->Actions->User defined Defaults.

2. Create a record  for your model.

3. Inside name place your filed name(account_id).

4. Inside model place your model name(account.invoice).

5. inside Default value  place the default value (id_number)