Hi.
What I understand from Your post is that You control the FOH sound from the stage?
Any good modern and/or vintage FX unit can be controlled via remote, with MIDI or simple switches. On some MIDI controlled ones You can assign several parameters to be controlled by volume pedal also.
With a simple UP/DOWN/BYPASS 3 button stomp board Your singer can change the programmed reverb patches up or down according to the song and mute the reverb during the occasional joke or two between songs.
Alesis Midiverb family comes first to my mind, there's plenty of them available, they're cheap and of reasonably good quality.
Then again, for rock IMHO You need only one vocal reverb throughout the gig and a single bypass floor switch would be enough.
Just my 0.02€
Sam