I got hit by an unapproved DCC charge at a Costa Coffee at Singapore airport a year or two back. I submitted a chargeback for the difference between the correct and DCC rates (which was something like 25 cents) and it was accepted by the bank.

Unfortunately I suspect the bank simply wore the charge rather than actually charging it back to the merchant which was what I was trying to achieve...

I don't know if Chase allow partial-chargebacks, but if they do this might be an option.