There are several approaches you might take for this.
The Verve 12Ma corrective IR was basically created by EQing the speaker by ear until it sounded "right", and then creating an IR from the EQ. To do this properly you have to understand where EQ is useful and where it is not, or at least have a very good ear. EQ alone may not get you close enough to your goal.
You might want to download a copy of Room EQ Wizard from the
REW forum.
If you send a sine-wave sweep through the speaker and capture the results, you can deconvolve (use
Voxengo Deconvolver) those results with the original sweep to create an impulse response. If you stop there you have a method of making an FRFR (well, a better FRFR) sound like your RCF, which is the opposite of what you are trying to do. What you need is the inverse of that IR, which will make your RCF sound like a better FRFR, or at least that is the idea. There is a program called Signal Wizard that an do this, at least in theory. The program itself is free, but the hardware that goes with it is not, and it's not clear whether you actually need the hardware for this function. I played with it a bit and didn't get anywhere, but it might be worth a look.
THIS PAGE has more information. Let me know if you figure it out. Really.
It seemed simpler to me to just write a program to create an inverse IR than trying to figure out Signal Wizard and do all of the data conversions required. I've made a good start on it, but have no idea when it might be finished.