Hi
I have e93 2007 pre 29.2 335i but upgraded with last firmware... so now turbo lag
Here in europe as well no way to have an hardware solution and back to old firmware.
But i did a little modification to reduce the turbo lag:
Simply bypass the left (the most close to rear of car) boost control solenoid by simply disconnecting the small pipes and connecting them together.
This mod is reversible and invisible. It will close partially the wasgates at idle...
No failure codes, running this since 2 weeks now.
Try and let me know....