Can I build a Zwift workout without riding or being paired to my bike?

Yes you can! There are a few ways to build workouts without being paired to your bike's sensors or actively "riding" in Zwift. 

1. The first and easiest, is to log into the Zwift application in "Fan View" (click "Just Watch" at the intro screen instead of pairing up your sensors and clicking "Ride"), then while in that view-only mode, hit the 'E' key on your keyboard to open the Zwift Workout Editor. From there, you can build your own custom workout without actively riding on the course.
2. Since these workouts are just simple XML files, you can build them by hand using any text editor. Just go into your Zwift workouts directory and create a new workout there with the file extension .zwo (for Zwift Workout) and the next time you launch Zwift, that workout will be made available to choose from the workout dropdown (or by hitting 'E' while in-game).

   If you're not sure where your Zwift Workouts are stored, there is a KB article describing all of the associated Zwift data directories found here:

   • Where is my Zwift data stored?

   Here is an example workout in XML format:

   <workout_file>
       <author> .MRBaldi Coaching </author>
       <name>The 300</name>
       <description></description>
       <tags>
           <tag name="INTERVALS"/>
       </tags>
       <workout>
           <Warmup Duration="600" PowerLow="0.2545" PowerHigh="0.75449997"/>
   
   
           <SteadyState Duration="300" PowerLow="1.0944999" PowerHigh="1.0944999"/>
           <SteadyState Duration="120" PowerLow="0.50449997" PowerHigh="0.50449997"/>
           <SteadyState Duration="300" PowerLow="1.0944999" PowerHigh="1.0944999"/>
           <SteadyState Duration="120" PowerLow="0.50449997" PowerHigh="0.50449997"/>
           <SteadyState Duration="300" PowerLow="1.0944999" PowerHigh="1.0944999"/>
           <SteadyState Duration="120" PowerLow="0.50449997" PowerHigh="0.50449997"/>
           <SteadyState Duration="300" PowerLow="1.0944999" PowerHigh="1.0944999"/>
           <SteadyState Duration="120" PowerLow="0.50449997" PowerHigh="0.50449997"/>
           <SteadyState Duration="300" PowerLow="1.0944999" PowerHigh="1.0944999"/>
           <Cooldown Duration="600" PowerLow="0.75449997" PowerHigh="0.2545"/>
       </workout>
   </workout_file>
   

That's it. Good luck!