What I did with the A320:
- I set auto brake to LO or MED
- RETARD RETARD = Idle
- When auto brake light is on, I slide down the throttle slider to ~-50%
- I maintain it until auto brake light is off
Doing this, it will auto brake with full reverses. The reverses will stop themselves before the end of braking.
If you slide down at 100% it disconnects the auto brake and brakes manually at 100% as if you were standing up on the brakes.
But yes a button for reverse would be cool...
FrankLFRS gave excellent advice to follow.
Most real world operators land with that autobrake setting. The RETARD callout from the the synthetic voice is a reminder, not a command so of course you decide how/when you choose to reduce thrust to idle. As long as it's idle when the mains roll on, you're good.
For autobrakes, there is a delay; to quote the infamous Airbus Notes by American Airlines Cpt. Eric Parks
Autobrakes are available on Normal Brakes (Green system) only. Hold pb for at
least one second. LO mode delays for 4 seconds after touchdown. MED mode
delays for 2 seconds. MAX has no delay. Do not use MAX for landing, MAX is
takeoff only (OM 3.12).
So with that delay being kept in mind, you just need to wait for the autobrakes to kick in before selecting reverse.
***Also, a personal technique that works well for me every time with the MED autobrake setting is to select idle reverse when I see the MED autobrake annunciation light come on. 2 seconds after the mains rolling on, the autobrakes kick in at the MED setting. At this point, I would begin to lower the nose. This is what I do with most transport type aircraft landings. With the A320 reversers using pivoting doors, it creates significant drag, even at idle application. So instead of applying slight back pressure to gently bring the nose down, I just time the deployment of the reversers in sync with the autobrakes and deceleration rate for a nice touchdown of the nosewheel
Here's the Airbus Notes if you'd like: http://www.airbusdriver.net/airbusnotes.pdf