Actually, drawing your weapon and chatting with him is useful
precisely because it lowers dispo by 10- it unlocks the disposition mini-game, so you can attempt it again, since he's no longer at a max disposition. So, if you're maxed at 56, draw your weapon. Now he's at 46- chat him up again. Repeat as necessary. Eventually the incremental gains will get you where you need to go.
Or if course, you can bribe him for chump change- an NPC's favor comes pretty cheaply.