Can you believe that the technique for a Vertical Reversement is clearly outlined in, of all things, a Cessna 152 Aerobats POH?I know this because I was flicking through one the other day trying to work out what the hell one was...it appears on the "approved manouevers" placard in the 152s I fly so I decided to look it up!
Anyway, from memory, the Vertical Reversement is basically a half snap roll initiated during a steep turn. Ie roll and perform a steep turn to the left, pull hard/stomp rudder, and the aircraft will start to snap roll. Recover from the snap and continue turning in the opposite direction.
I've snap-rolled 152s plenty of times so am keen to try one...