John Voorhees, in his review of the new update:
Workouts++ has come up with a solution that works surprisingly well given the audio API limitations of watchOS. It has a dedicated tab in the iOS app where you can subscribe to your favorite podcasts, which show up in the ‘All’ section of the tab. If you tap on an episode, it downloads and is transferred to your Apple Watch, a process which can take a while. The advantage of downloaded episodes is that there’s a little button on the Watch’s playback screen to skip ahead and back 30 seconds or one minute at a time depending on the length of the episode.
When you start a workout on your Watch, you simply swipe left once to display two sets of podcast episodes. At the top of the view are the downloaded episodes that play immediately when you tap the play button. The remainder of the podcast view lists streamable episodes. Tap one of those episodes and it doesn’t start playing until (at least in my tests) about 4 MB of data has been transferred to the Watch. The initial buffering doesn’t take very long on a good connection, but if you’re headed out for a run, the wait can feel longer than it in fact is.
I still want Overcast on my Watch, but this update from _David Smith is incredible, and the best part is that’s free.