We really shortened our practices but made sure to have some intense compete periods. The compete periods were non-contact though because we didn't want to risk injury before the playoffs. We used tug-of-war type competitions that were relatively safe but still intense. That kept the energy and enthusiasm high.
I think the very short practices along with high energy compete periods really helped us maintain energy and focus through the lull of the bye week.
That said, 3 consecutive bye weeks is crazy. I think keeping your players from drifting too far in to winter sports like basketball and hockey would be a huge concern in that scenario.