AKA get a five speed. It'll be alot easier and likely cheaper.It's common in the domestic world even with new electronic trannies.
I dont know what exactly can be done in the case of the newer electronic Mazda G4 series transmissions but if your brave you can start experimenting.
I doubt you can alter shift timing without hacking the PCU but you should be able to effect the pressure range the trans a fair bit before the PCU starts throwing codes.
Find the main line pressure regulator (it should be in the pump housing and is accesable in many trannies while in the car) and experiment with shimming the spring to increase line pressure.
Next you can find any restrictions put in place to modulate engagement/disengagement of the clutch packs and open up any drainage ports in order to create crisper shifts.
Then you might tear the trans down and add clutches where possible to increase holding power and overall stregnth and possibly installing larger servo pistons for the same reason.
Since it's difficult to change the fluid's PSI through the PCU you will be increasing the surface area that force is being applied to for a similar effect.
There is no fuel cut with auto cars as there is no lift during shifts.Actually I think it works for all the gears because it does away with the pre-shift fuel cut. I haven't had the nerve to do it, since I've been having enough trouble with the car as it is. It's really just a matter of cutting a wire, though. I don't think you actually mess with the VAF itself.