Here is one not so elegant but get things done way. Why not just load the original and replace the last FC layer?
Here is an example using the pretrained AlexNet in PyTorch.
model = models.alexnet(pretrained)
classifier = list(model.classifier.children())
model.classifier = nn.Sequential(*classifier[:-1])
model.classifier.add_module(
    '6', nn.Linear(classifier[-1].in_features, num_classes)

Hope it helps.