Max out TFC's impact so its a two headshot kill in PvP, increase accuracy and lower the amo reserve. That way it can be a special. Then add a perk allowing it to be equipped with the TLW as primary.
For added flare, make TFC a left handed weapon so youre switching between right and left hands.
Edit:
Lotsa misconceptions about what it would mean for The First Curse to be used in this manner. Check discussions below. It wouldn't be Halo/Perfect Dark style dual wielding and The First Curse would def NOT be OP like this. I also think you should be able to choose between a primary version and special version.
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I think that'd be pretty neat, but I don't know how you'd fan the hammer if you were holding two guns.