I don't know if those drives you guys are using support it or not, but the best method, IMHO, is to use slow down limit switches, which reduce the speed of the motor considerably when made, then allow the motor to go slow until it hits the stop limit switch.
I toyed with the idea of using that on my mrotate, but there didn't seem to be enough interest in it at the time.
Of course another way would be to use timers in the software.
Example: drive gets horizontal command, motor starts and timer starts. After a few seconds, when monitor is pretty close to the horizontal position, timer times out and motor goes to low speed until the stop limit is made, then motor stops and timer resets.
This would be the simplest way to do it. I don't like using timers to control motion, since things in the real world changes, and time needed may change, but in the case of giving the monitor a slow down point, I suppose it would be ok, I mean you still have the stop limits if something goes unexpectedly.