Maintaining Boost Between Gear Shifts

I'm running a relatively laggy turbo on my EJ20 powered Subaru and have been using a flat-shift in order to minimise any significant drop in boost pressure between shifts.

While this works to a point, I'm wondering if there are any alternatives that may be more effective?

I've considered a regular shift and modifying the ignition map to create a portion in the high RPM-low pressure zone with the timing retarded as -5 degrees on my launch control yields a substantial level of boost.

If you close the throttle there will not be enough energy to keep the turbo spooled. You would need antilag setting for DBW or a throttle kicker or large bypass for a cable throttle when you had antilag active.

Ok so anti-lag would be my best option? The functionality is there but I never looked into it as I was hoping to find a solution that would not affect other driving conditions and idle, except for during a drag race.