While it is usually the norm to flash in SU binary via a custom recovery, they are two different things entirely. So, yes there is a way for you to do that without having to install a custom recovery. However, if your only reason for not doing so is so that you will be able to install the OTA updates, well you should know that people usually post the OTA updates 1 or 2 days after they have been released and they can be flashed in via the custom recovery. So there should be no worries on that part. Also, sometimes having root causes the OTA to fail and not update or in some cases it even removes your phone's root privileges. Anyhow, as for your answer, I assume you're familiar with how to work with adb binaries on your computer. So just download the su.apk for your phone (Google it) and simply paste the SU file in the adb folder. Open a CMD window in that folder and type the following commands (will only work with s-off)
adb remount
adb push su /system/xbin/su
adb shell chmod 04755 /system/xbin/su
That's about it. Oh and you will have to install the SuperUser app from the PlayStore after doing this.