The solution is extremely simple. You see, Pakistan would already know where are these missile batteries stationed. Even though these are mobile SAM systems, they aren't exactly the shoot and scoot types. It takes time to wrap things up, disconnect the power generators and etc and move. Until everything is wrapped up, the entire battery is staying put. And THAT is the S400's (or the S300's for that matter) Achille's heal. Pakistan already possess armed drone technology and they possess a pretty long range, long enough to penetrate deep inside india. These drones are far cheaper than even a single S400 missile and thus can be produced (and launched) in overwhelming numbers. Do you see what I'm getting at? We will use this technology to basically produce CANON FODDERS! When a war breaks out and india deploys the S400s, they will instantly be faced with a catch 22 situation. Do they waste their expensive S400s on these cheap but deadly drones that are heading their way? Or do they save the S400s for the real threat of SSM missiles? Either way, they will be destroyed. Because if they waste the S400s on the drones then battery will be effectively helpless against the Pakistan's SSMs and the PAF strikes. And if they don't shoot at the drones then naturally the drones themselves will destroy the S400 batteries. Basically a "damn if you do and damn if you don't" kinda situation.
PROBLEM SOLVED!