boot loaders and USB devices

[Aiza]

My PC does not have the BIOS option to boot from USB.

I use an USB cabled external hard drive for taking backups. It has 
FreeBSD installed on it which I want to boot from so the motherboard 
cabled hard drive file systems are un-mounted during the dump. This USB 
drive will only be attached to do backups.

I also have a USB stick containing a Freebsd install used to clone 
itself to the motherboard cabled hard drive.

Since the BIOS will only boot from the motherboard cabled hard drive can 
I install a boot loader to gain boot access to my seldom connected USB 
devices?

I reviewed the grub port but with no joy.

What do you recommend?