[syslinux] chainboot from grub to syslinux in logical partition

[Cynthia Flynn]

For reasons I won't get into, I need to use grub (not grub4dos, super 
grub, or any other variant) as multiboot loader on a USB thumb drive, 
but I also need some of the partitions to contain bootable content from 
syslinux-based ISOs. All of these syslinux partitions must be logical 
rather than primary partitions and they will not be the first partition 
on the drive. Porting the syslinux configuration menus to grub is not 
possible nor desirable in some cases (think Ultimate Boot CD as one 
example).

What I was hoping to do was retain the existing syslinux configurations 
as is and simply chainboot from grub to syslinux the same way I do to 
pass boot control from grub to the FreeBSD boot loader.

My thinking is that this would be possible if I could get syslinux or 
some other utility to write a proper volume boot record to the logical 
partition's boot sector without altering the thumb drive's master boot 
record. I think that when syslinux installs are done that ldlinux.bss 
and ldlinux.sys are patched according to drive/partition-specific 
attributes and ldlinux.bss is then written to the boot sector, right?

But, in Windows XP it is not normally possible for syslinux.exe to even 
see anything but the first partition on a thumb drive. Moreover, 
syslinux.exe would overwrite my MBR. And is it even capable of writing a 
VBR to a logical partition anyway?

I know there's a tool called makebootfat, but it isn't clear to me that 
it can be made to leave my MBR alone either and I don't think I can 
point it at my logical partition either.

So, is there a way to produce and install the correctly patched 
ldlinux.bss and ldlinux.sys files appropriate to the destination logical 
partition such that its VBR can be directly and successfully chainbooted 
from grub?

Cynthia