Originally Posted by
msu2001la
The easiest way to do this is within Zwift. Make a custom workout set to whatever wattage you want. Use the trainer in ERG mode and it'll keep you at that wattage.
How to Build a Custom Cycling Workout - Instructions | Zwift
You can still watch a movie on the same device that is running Zwift - just have it run in the background.
If you want to gain extra xp, instead of making it one long workout block at whatever W, you can make it a whole lot of 1 minute blocks of that power. If you're able to stay within range of that power, you get xp for each block you complete.