Hello,
I've create a plugin which restrict 1 middle shot for exemple for de_dust2 on middle 1 shot per person, for that u need only upload the plugin and create zones thanks to devzones from francisco and rename zone middle, middle1, middle2 etc..
This plugin will detect every shot from sniper, i've test it on CSS, but the weapon is check too on CSGO.
Sorry for my bad english, if u have any question i'll answer u