[syslinux] installing extlinux on image files

[aep]

Hi,
is there any way to install extlinux on a _not_ mounted ext4 image?

I can easily write the extlinux.sys manually to a fixed inode, and 
prepend a  prebuild mbr, but is there anything else i am missing? 
patch_file_and_bootblock does a couple of magic things, that are beyond 
me.
The devices are simple images that run in virtualbox, so do i really 
need all of the blocksize magic?

thanks.