Do what @wescaine says. 
Here’s my post describing all four Fitness Test workouts –
From old trainer to smart trainer. Set FTP - Training - Xert Community Forum
A bit OT but it relates to BTs and Slope mode –
I have switched to riding many of my HIT workouts in Slope mode on EBC instead of AUTO.
Or at teast the hard set portions of the workout in Slope mode.
When you do this it solves several issues.
First off there is no trainer-response gaps since you apply power immediately by switching gears or spinning up.
Secondly you’ll never experience the spiral-of-death from ERG control if you falter on an interval. You can’t really fail a workout either. While you may not have complied to all intervals and taken some extra breaks, you can complete the workout under your control. If I have to skip any intervals I also have the option to insert some of my own to acheive the low/high/peak targets for the day.
Lastly there are opportunities to go for a BT whenever MPA is drawn down enough for you to try and push throught it. The EBC rainbow gauge will let you know when you’re close. If you feel up for it, go for it. Or consider those tough moments as proof your signature is dialed in.