I have no idea how it is done with grub - I am thinking of figuring it out - but I reckon it is may not be easy.
But it is possible to change - although not a trivial change.
It requires switching the system use a unified kernel EFI and other changes to system configuration.
Perhaps not a good first issue - if you know what I mean 
I created a proof-of-concept topic a while back - mostly targeted secure boot - but you can leave that part out.