but Arduino team do not know this ? when it create the "Upload via Programmer" tab/option i test it (i write a guide on it in my sign) and discover that this command do not work on Mega.
I do not know if we must manage this behaviour like a Bug, (bug on Mega, or bug on Uno, depend what the team means whit Upload via Programmer)
I think the team wants to exploit the behavior of the ProgramCounter on the UNO, so the team do not want that the user must change the Fuses, but did not realize that this trick work only on the 328 
What do you think ?