In lieu of an attempt to decrease the chain line at the front, maybe first try a thin (1 mm or thinner) spacer behind the cassette to increase the chain line at the rear? This assumes that the cassette lock ring is deep enough to securely engage the freehub and no clearance issue between the chain and the right chain stay after shifting the cassette to the right by 1 mm. At least it would be an inexpensive potential solution.