I don’t think there is a practical way to do that. However, if the route isn’t too hilly (long or steep climbs) you can can free ride to a target Focus as the alternative to structured intervals. That is the advice on the left side of the ATA panel.
Focus Type: xxx (minute mark on power curve)
Interval Target: xxx Watts (rough target at any duration required)
Workout Goat: xxx XSS
The key aspect is you are free riding to a Focus target that you can monitor at any time.
It’s kinda fun once you learn how and is a different way to ride the same route with varying results (Rating, Specificity, Focus).
20 minute mark and higher are Endurance rides. Go as slow and easy as you can depending on the terrain. Highest I have gotten is 43:00 minute mark by riding out and back legs that are flat. The key is to start slow then continuously pedal at low intensity (lots of gear shifts) and avoid all hills. A stiff head wind could mess things up. 
If you are successful Xert EBC will title the activity “Easy Polar Endurance Ride”.
Below 20 minutes is where it gets interesting. For example, driving Focus down to the 4 minute mark range is a hard ride that will end up titled “Difficult Mixed Puncheur Ride” or “Breakaway Specialist” if closer to the 5 minute mark.
I normally try to punch it down rather than ride longer intervals at target watts. I am not good with long intervals but don’t mind hard repeats especially when descending or on a gradual climb. In either case you’ll be beat by the end of the ride.
Coasting during RIBs helps keep the Focus number down since riding at 0 watts means no low strain minutes. Pedaling easy between efforts will raise Focus but that’s unavoidable at times.
If you hit your XSS goal with plenty of distance left on the route don’t worry about Focus rising back up. You’ve met your goals for the day and extra XSS at low intensity is a bonus similar to an extended cooldown after an indoor workout.
Range of activity titles –
Rating: Easy, Moderate, Difficult, Tough
Specificity: Polar, Mixed, Pure (unlikely outdoors)
Focus: 2 min (Road Sprinter), 3 (Pursuiter), 4 (Puncheur), 5 (Breakaway Specialist), 6 (Rouleur), 8 (GC Specialist), 10 (Climber), 20+ minutes (Endurance)
I cannot imagine what a Difficult Pure Pursuiter Ride would feel like if that’s possible to do. YMMV 
Reference –
Understanding ‘Focus’ and how to use it – Xert (baronbiosys.com)