Don't seal the pipe!!!

On an EsCos it's a 'Lektron' valve - it's a 2 port version of an amal valve essentially, and is controlled by the ECU for closed loop boost control.

When I took the cone filter off and replaced with an airbox on mine when I bought it, the boost needed tweaking.

What Pop's said would seem to be the easiest solution, although boost may still need tweaking slightly.