Apologies for the upcoming info dump, I do not have that much to offer here but something might be of interest.
Not that it is strictly relevant here but if my memory serves (and it has not been brilliant these last few days) the EZ4 used a NOR- SRAM chip for the loader and well SRAM and then another bigger NOR chip for the NOR that we all call the NOR section.
I did once mess around with the loader section patching in a few parts of the header- either tweaking a few ASCII strings or straight up copying the header from the EZ4 loader to the old EZf3me (darkfader made a quick loader for DS homebrew on the NOR) and somehow managed not to brick my cart.
Likewise the EZ3 loader assuming the hardware holds is just in one of the subdirectories of the EZManager program- perhaps a bit of patching and poking around can see you using the EZ4 one instead.
On that matter as well it might take a bit of digging but cory1492 did once dump the very first EZ4 loader (the one that still had the EZ3 fishes skin), it barely works for anything but it might help if you can find it.
There is also a EZ3 standalone reformatting tool called EZcheck
http://ezflash.sosuke.com/viewtopic.php?f=2&t=531
I have not poked around it yet but it is a barebones flashing tool for the EZ3 that sets a basic loader on the EZ3, it is standalone so I assume there is a payload in the exe itself if it comes to that level of fiddling.
@how_do_i_do_that if you find some unbricking stuff do share- I only know of what I wrote up above (cory1492's stuff)
re Yoshi island NOR- you should be able to write any GBA rom to the NOR these days just by pressing select on the rom when it is on the mini/micro SD. Before you might have had to pad it.
If any of you need something from a working EZ4 (I have an EZ4 miniSD and a plain EZ4 lite) I still have my EZ2 linker and software working here, it is only the first style EZlinker though so it might not be ideal (there were three main types- 1 for the old EZ1/2, one for the EZ3 and another that you could "program" to use either).