Booting Live openbsd image on fat32 media

[Mohammad BadieZadegan]

Hi everybody
I like using OpenBSD on every situation but need to booting OpenBSD image
on my FAT32 media.
In other words I have USB Flash (32GB) memstick that its file system is
FAT32 and I want to install a boot manager (Like GRUB or Grub4DOS) and then
How put OpenBSD image on it that don't curropt its file system or booting
OpenBSD?