This has been done and it fairly common among drag cars. Generally you put the turbos before the supercharger. You can't Y them together, the pressure the supercharger creates will just leave out the turbo, and since its flowing backwards through the compressor would pretty effectively stall the turbo out so it will never make boost. I've only seen it done on V8s, and I don't know what types of superchargers are available for 4cyl engines. What is done on the v8 drag motors is they'll put a roots blower on top:
The roots blower is the big ribbed box with the thick belt driving it on top of the motor. The turbo(s) feed into the top of this, where the carbs are on that motor. The reason this works so well is the roots blower is a positive displacement supercharger, meaning for 1 turn it always pushes the same ammount of air. So before the turbos are spooled, it sucks air through the turbos, compresses it, and feeds it to the motor. The increase in exhaust will quickly spool the turbos, which then increase the pressure between them and the supercharger. The supercharger then takes in a big gulp of the pressurized air, compresses it further, and feeds it to the motor. So if you're running a blower that gives you a 2:1 pressure ratio without the turbos(1 bar boost), and turbos that give you a 3:1 ratio(2 bars boost), you'll have a combination that'll potentially produce 5 bars of boost, or around 70psi. Not too shabby... you can probably do something similar on the street, but in order to gain any low end, you need to use a positive displacement supercharger, which basically means either a roots type or a screw type(aka whipple, lysholm type). The problem now becomes you may be producing too much pressure since its a sequential system. If set the supercharger up to run 6psi(1.4:1 pressure ratio) and wastegate your turbo at 6psi, you'll end up with a total pressure of around 14psi.