It is not possible to increase the boost of turbo #1. Both turbos share the same wastegate. When turbo #1 hits 9 PSI, it then sends some pressure through the VSV in order to prespool the #2 turbo. When #2 turbo comes on line, both turbos are working together to make your maximum boost. The only way to get both turbos to boost faster is through a True Twin Turbo Conversion. Downside, is that many find it too laggy on the Automatics. I only use this conversion when I'm racing from a roll. Otherwise I keep mine in Sequential the rest of the time.
Peace,
Jesse