After doing some research over the last three weeks, I purchased an accelerator for the Amiga 500 that claims to be able to boot to large IDE partitions from AmigaDOS 1.3.
HC533 33MHZ 8MB RAM IDE Turbo Board
The "Oktapussy" and "Oktagon" are boot ROMs and one enables support for IDE and large partitions.
The only downside of this accelerator is that there is no disable mode for the extra ram or the acceleration, so whatever you put it in will be mostly for WHDLOAD and not booting older games, although the list of games that don't work with fast ram is quite small.
It isn't too much of a stretch, this is how early VGA cards and early IDE controllers added support and how modern XT-IDE flash cards work today. Remember seeing old PCs boot with "VGA BIOS?"
I will report on whether this works well when I get around installing it