Pulley swap?

Don't know how much that gains though, the stock blower may be pretty taxed already.

If you go really aggressive on the pulley, then you'll severely shift the torque down the rpm band, giving a diesel like curve. But you'll destroy your top end (or blower). Seen guys do it to Cobras. They'll make a flat curve at 500+, but hp tops out at 450 or so.