U mean 2 ceasefire on ur ally.? Because it u r on neutral stance with a faction u wont have a "ceasefire" option anyway.
Otherwise if u r on "war declared" stance with a faction it doesnt matter wheather ur fighting battles with that faction or not, it is still the same.
Even if ur enemy is not fighting u they might b fighting other factions at the same time, maybe more factions than they can handle. So if u offer them ceasefire they might accept...