Build a warlock /click macro.

It will attempt to execute every spell in the click at once.
With a priority system, Immolate will fire off before Conflagrate attempts to.

Baring resists, you will never attempt to Conflagrate, without Immolate being up.
Similarly, the fall through Incinerate will always have Immolate up too.

While leveling, maybe 2 or 3 mobs in 100 will resist any given cast.
So you're not really losing all that much.

And once you are 80, hit gear is fairly easy to come by.
You don't need a whole lot of it, to be hit capped for heroics.
And if you can do heroics with your team (you will with tank + heals + dps), you can get hit capped for raids, if you want to raid.

Once you are hit capped for your content, your spells will always land every time.