If you speak to Doobrey over at Amiga.org then he can tell you.
He created these tools called Romsplit and Remus for manipulating kickstart images.
People have recently been able to create KS3.9 ROM images (with the ROMUPDATES from AmigaOS3.9) and add extra things such as drivers to enable booting from CD drives etc.
http://www.doobreynet.co.uk/flash.html
The files on his website are not the latest, pm him for details.
With an EPROM programmer and these tools you effectively have a kickflash equivalent.