[Lolzytripd]

to the best of my attempts of finding a way to do it with 7m.

There is no way for a demon hunter to engage a wild ride on their own, only using tools from the demon hunter class/soldier reliably.

DH
Leadtempest>descending ouroburos uses 7m
Reaver's KD also knockbacks, also costs 3m, and only KD's if both the enemy and the user are airborne.
Desperado KD's with shotguns only, Shotguns knockback, this becomes an issue since wild ride is only usable on enemies in one range.
Matador's bellowing stag knockbacks and KD's making it unusable to wild ride with.

Soldier
Charge strike turnover consumes all momentum.
Flatfoot charge bash +earthbadge has a 50% success rate of KD.