Provided your turbo can take it......

ALS works.... (simplified explanation)

When the throttle is closed or nearly closed, an auxilary air valve is opened
to allow a large air flow into the engine.
(Usually an extra or modified idle speed valve)
During this time, a boost limit and an rpm limit are set.
EG. 0 to 10 psi, 5000 rpm (only as an example)
Also, during this time extra fuel is added (about 5-15%) and the ignition is retarded
past TDC (negative advance 5 to 30 degrees)

The result is once enabled and the throttle is closed,
the engine revs high at a limit and the ignition retard and extra fuel continues
burning in the exhaust manifold making the turbo spin as if you were driving.
This creates a small amount of boost or keeps the boost high during gear changes.
Also a poping/banging sound at the exhaust which most people like !!

The draw back is, the turbo, exhaust valves and exhaust manifod experience VERY
high temperatures which could easily damage them.
If not set up correctly or the wrong components are used, it wont last long.