Similar boat as you - '19 Rebel here and after jogging through all the menu options, without pulling a fuse, I've seen you can only manually choose between aero and normal at all speeds.
Anything greater than 27mph in Off Road Height will self lower to normal, anything faster than 17mph will self raise from entry height (either up to aero or the last setting if entry mode was hit with the keys)
... If you find or devise a solution, definitely post up!
The closest possible option I saw a tutorial on was to use a relay triggered by a spare home link button to 'disconnect' the fuse (f70?) Temporarily when needed.