There are a limited number of players in my area, and the other most available player will only ever play "to the death!!" as a game, which is the most boring of games in my opinion. I need some more convincing arguments to bring them aroound to objectives or really ANYTHING ELSE.
Have you tried playing your current mode with something running along side?, like a capture the tower or one me and my son play is a treasure chest with random gifts in it, some good some bad. Or ask your opponent to come up with an idea and slowly tweak it too get something your both happy with.
Make it campaign like. You can still fight to the death but have several objectives throughout (hold the terrain for 3 turns, kill the general, etc.) Each objective gets a bonus next game.(one game 5 up ward save for general, +1 for roll off between turns, etc.) Eventually the objectives will become more important than an annihilation.
Try challenging them! I mean, you can say to one of those players "Ok, we have already battled face to face... but I BET you can't defend that hill (as an example) for 4 turns if your army is 1/3 of mine!". Or viceversa: "Try to get the treasure in that building I am defending with my Temple Guards before the 5th turn: you can field three times my models count, but if you can't reach it in time I can put in play Lord Kroak". I would accept immediatly to play a game like this... Or maybe try to imagine a sort of narrative scenario, like "In the Realm of Life, a comet has fallen in the middle of a dangerous forest [your battlefield]. Some say that the heavy metal hidden in it is used to forge indestructible armors, others that it's a source of arcane and deadly magic. What is sure is that any race wants that celestial thing. [so anybody can play his favourite army] Now, two [or more?] opposite factions fight for the control of that strange object: who will be able to steal it from the hands of his rival, and bring it home without succumbing to the enemy's greed?" This "battleplan" would consist in a sort of tug of war for the control of the comet: with some little modifications it might turn into a funny game, enough different from the regular battles to be interesting, but enough similar to regular matches to seem suitable for anybody! [Don't know if I answered properly your question, but I think there's not some sort of convincing argument to make someone play in a particular way ]
I mostly play 40k and for years I only ever played "annihilation" games with my regular opponents, and they always wanted to play with huge armies. The way I convinced one person to expand was to have a series of linked games - first game was around 1000pt worth and a simple objective game, game 2 was 1250pt with more objectives and just to top it all off with an epic battle we had game 3 as a 2000pt murderfest. My new regular was easy to get into objective games. We played a tournament, we were ill prepared for objective based scenarios and we got smashed. He's a pretty competitive fellow and ever since then we've played proper missions.