I know I've done this in the past, but I don't remember how.
I have a Windows XP installation on the primary partition of a HDD, with unallocated space after which I can use for a Linux partition to contain frugal puppy files and GRUB. I don't want GRUB to touch the MBR. I'd like to have GRUB's IPL (stage 1) on a Floppy pointing to the stage 2, etc. on the Linux partition. Then set the BIOS boot order to Floppy first, HDD second. That way if the floppy is present it will boot Puppy, and if the floppy is ejected, it will just boot Windows normally. This solution has worked well for me in the past, but I don't remember how I did it to replicate it!