I currently run a Belly Drum/Earthquake/Fire Punch/Double-Edge variant myself, and a Blazed Fire Punch manages to actually wreck quite a few things, even things I didn't suspect it would like Gyarados (non-bulky version..unless you have Stealth Rock up, then it'll never be a problem even with Intimidate) and Salamence (again, running on the assumption that it has 4 HP EVs and 0 Defense EVs...which most, if not all, run). It's a shame you didn't get Fire Punch on it before you transfered, that's obviously its best attacking option this gen...though I still continue to wish that the Fangs had a BP closer to Crunch than to Bite.
Anyway, given your current circumstances, I would say go ahead and stick Earthquake on it. It's always been the typical BellyZard's bread-and-butter attack (well...before Fire Punch).
Actually, I highly suggest that if you have the time, patience, and resources for it that you should go and breed another one, and make sure this one learns Fire Punch as well as Earthquake for its second attack. It'll be your best friend once Blaze is active. Still have to watch out for Bulky Waters though without the aid of Double Edge.
I would've suggested Rock Slide in here, but considering how risky BellyZard is to pull off anyway, the notorious miss rate is something I don't want to fool around with when you're basically running on 1/4th of a full tank.
EDIT #1:
Just telling you, it will be really hard to pull off. I mean, Stealth Rock already chips off 50% of Char's hp, plus another 50% is a dead Char.
Oh, and this response = epic fail if you make sure to get odd HP. It's not the best Pogey in the game by far, but poor Zard doesn't get enough love because of those raving fanboys and the ZOMGSTEALTHROCKWEAK! that people can't seem to tear their eyes off of (which is true, but any competent BellyZard player can and
will work around that if at all possible, so it's overly presumptuous to think that just because you laid Stealth Rock out that Bellyzard = dead. I've had quite a few cases where Stealth Rock worked to my benefit). But don't misunderstand me, Stealth Rock is still a threat to it, but it can be avoided with proper precautions.
EDIT #2:
Well now, I never thought about using Fly, but seeing Firestorm's last post, it makes sense. With it's power bumped up to 90 and STAB, it's more powerful than Double-Edge, so it should still be able to KO the majority of Bulky Water types save Suicune (which Double-Edge could never do anyways). Fortunately, Suicune doesn't seem to be getting alot of love this gen.