如何在没有显式model.fit的情况下设置tf.keras.callbacks.ModelCheckpoint？

import tensorflow as tf
from tensorflow.keras.callbacks import ModelCheckpoint

model = tf.keras.Sequential()
# 添加模型层
...
model.compile(...)

checkpoint_callback = ModelCheckpoint(filepath='path/to/save/model.h5', 
                                      save_weights_only=True, 
                                      monitor='val_loss', 
                                      mode='min', 
                                      save_best_only=True)

model.fit(x_train, y_train, 
          validation_data=(x_val, y_val), 
          epochs=10, 
          callbacks=[checkpoint_callback])