I'd have to assume that mepis allows you to install it's bootloader to it's partition.
I always install any other distros bootloader to their partitions.
Running
from ubuntu should then find them.
If it's not found then you can create a custom grub entry in grub2 to allow booting the other install.
Edit - a quick look at a mepis install page
http://www.mepis.org/docs/en/index.p...RUB_Bootloader
Install grub to root rather than MBR and you should get it added to ubuntu's grub with the update grub command