In the tutorial, the backbone is created using model.features.
This is unfortunately not possible in the current Inception implementation, since some functional calls are performed in the forward method as seen here 26.
These functional calls also make slicing the model and wrapping by nn.Sequential not possible.
A possible workaround would be to return the features, by replacing the last linear layer with nn.Identity:
model = models.inception_v3(aux_logits=False)
model.fc = nn.Identity()

This would not slice the model in any way, keep the forward definition, and just return the penultimate activations.
Let me know, if this would work.