How to install Grub on SD card?

I want to install grub on SD card because my laptop don't boot from external sata port. I've the SSD connected to the laptop through the external port sata to make it easier for me to boot the operating system also on my desktop. I would like only to have to install grub in the SD, but maybe the only solution is to install linux on the card just to modify the grub configuration and be able to launch the existing operating system on the ssd disk. I'll never use the OS written on the SD. Is possible setup grub on SD card? Thanks