System update but rooted

Okay so I have the bootloader unlocked, rooted, twrp and running ex kernel. I had system update turned off in disable services but then the phone wasn't going into deep sleep was always running at 300 mhz. So to fix that, I turned system update back on ... great I get deep sleep back but now they released the update for stage fright and I get a message that it is downloaded and ready to install.... I tried the install even though I knew it would fail... it goes to twrp recovery. So how do I keep the system from trying to update? I know I could in theory flash the stock recovery let it update and flash back to twrp... maybe.. but I am hoping there is another route since I plan on flashing the M factory files when they come available...