Fire is the melee set that requires the less recharge to have a great chain : GFS/Crem/Inc/FS (133% in GFS, 72% in Inc, 35% in Crem). It's almost as good as GFS/Crem/Inc which has a tad better dps, but requires alot more recharge.
In your case you might not have the recharge to reach those. But it's a good thing to know for your end game build.
Something like GFS/Scorch/Inc/Crem/Scorch has also a very nice dps and just requires 102% in GFS, 52% in Incinerate, 20% in Scorch, 19% in Cremate. If you have just a few global recharge like 15-20% and a good frankenslotting in your attacks it might be attainable in the low 40s. Even if you fall a bit short of recharge on GFS, a low gap is not that much a problem for a leveling build.
If you dont mind lowering your dps alot, and want to use boxing as a filler with only 3 fire attacks, look at something like Inc/Boxing/Crem/FS/Boxing. It still requires 68% in Incinerate, 35% in Boxing and 32% in Cremate.
My opinion is that having some gaps in a single target chain while leveling is not a huge problem, it's the reason I usually more focus toward end game chains.
I might not have found your dream chain, but I hope I gave you a few ideas 
Edit : I found another one that is worth considering too, Inc/Scorch/Crem/FS/Scorch, 76% in Inc, 62% in Scorch, 38% in Crem. Good luck !
Ok basically I have a fire/sd (33 atm) and I'm trying to minimize how many attacks he has. Problem is I'm not going to have any global recharge on him for a while (although I could maybe swing 10~20% if that actually made a diff).
I'd love to run only 3 attacks but only if it's close to the DPS I'd get with 4. I'm not going to get the recharge for Inc/Scorch/Crm/Scorch anytime soon though. I will have Boxing in my build if that matters at all.
Any help would be appreciated.