This is a repost of an archive I posted in 2015.
This method works for DSM 6.2 using Jun's loader 1.03b for me.
1) Enable SSH and ssh into your DiskStation
2) Become root ( sudo -i )
3) Make a mount point ( mkdir -p /tmp/mountMe )
4) cd into /dev ( cd /dev )
5) mount synoboot1 to your mount point ( mount -t vfat synoboot1 /tmp/mountMe )
6) Profit!
admin@DiskStation:~# sudo -i
root@DiskStation:~# mkdir -p /tmp/mountMe
root@DiskStation:~