Ah, thought it'd only be needed for specific levels, that's seemed to be the case in SMG2. To hotkey it, I think you'd only need to change the code for the current fog toggle in Frame.cpp but that'd be a pretty quick and dirty patch 
else if (IsHotkey(event, HK_TOGGLE_FOG))
{
OSDChoice = 4;
g_Config.bDisableFog = !g_Config.bDisableFog;
}
to
else if (IsHotkey(event, HK_TOGGLE_FOG))
{
OSDChoice = 4;
g_Config.bEFBAccessEnable = !g_Config.bEFBAccessEnable;
}
or even something that toggles between something like auto IR with no EFB Access, and 1.5x or 2x IR with EFB Access.

else if (IsHotkey(event, HK_TOGGLE_FOG))
{
OSDChoice = 4;
g_Config.bDisableFog = !g_Config.bDisableFog;
}
to
else if (IsHotkey(event, HK_TOGGLE_FOG))
{
OSDChoice = 4;
g_Config.bEFBAccessEnable = !g_Config.bEFBAccessEnable;
}
or even something that toggles between something like auto IR with no EFB Access, and 1.5x or 2x IR with EFB Access.
