pali, I've added an option to select only partition or even a file to write into Check revision 98+
I just tried it with a file target and it finished in less than 10 minutes on default options. This way you have to make sure the image is bootable yourself, obviously. Also, there are experimental bootmenu .item generation, check it and remind me please, where should we put it?
Note: I've created a file for the image with