Chords with alternate bass notes

Hi there.
I’m new to this website/app, so I’ve been testing the whole thing for free today.
There’s one missing feature that I’d like to see : I think it should be easier to add an alternate bass note to a chord. I know there’s already the “inversion” function, but I don’t think that’s enough. Writing something like a chromatic bass walkdown, or even a chord sequence like Ab/Bb to Abm/Bb to EbMaj7 (a nice classic minor substitution on a V chord in Eb major) is impossible, because Abm/Bb doesn’t exist in the database.
What do you guys think ?