This time nvidia hasn't released any maxwell cards for Mac. So you wont find any public roms for maxwell.
MCV flashes/sells 750ti with EFI ROM (BootScreen on non-4k monitors).
So it is possible ... and not so expensive ($80.00 / $225.00) but it's absolutely not funny

.
What needs to be done is more or less the same as for
GTX770 :
Primary challenge is changing device I'd in BIOS and EFI.
Modern Nvidia EFI has 5 functional sections.
1. InFoRom image
2. PC BIOS
3. EFI/UEFI
4. Some weird section
5. Security certificate
All 5 sections need to match for card to work in Mac and Windows.
Probably easier to start learning on Fermi as they only had 2 parts but many
EFI changes and BIOS changes are similar.
I will give a warning, with KEPLER and Maxwell if you make changes to rom that are t properly reflected in the InFoRom inage, it may let you flash the card into a non-functional state but then not let you flash it back, giving the message "failed to merge inforom image". If you do not have means to erase EEPROM you have created a "brick".
Better to start with Fermi.
GTX750ti PC Bios (Maxwell) :
LinkGTX680 Mac Bios (Fermi):
LinkGTX680 PC Bios (Fermi):
LinkI'm also interested in this feature, I will give a closer look later on ...