This should be it:
dd if=koboimage.img of=/dev/mmcblk0 seek=543745 skip=543745 count=524289
this is assuming two things:
-the first one, the image you're copying from is a complete image of an internal sd card so it has the correct offset for the recovery partition, it is called koboimage.img and is stored in the current directory;
-the second one, your sd card taken from the kobo is attached to your computer and being recognized at /dev/mmcblk0.
Especially the second thing could not hold true, please check and be careful this device actually belong to the sd card and adjust accordingly.