Could I use lemmi to adjust the stock ecu's A/F so it doesnt run lean. Would it be drivable?

 

The problem with using the stock programming is that the timing and fuel curve are nothing like they will be with a larger turbo and injectors. If you drop the boost down and run off the wastegate, you should be alright, but you would need to use the stock maf and injectors. Just dont run more power than the injectors can handle