This is how I would do it:

Have the paladin as your "main" toon, i.e. the one you control.
On the warlock set the paladin as your focus.
Change your warlock's spells to macros, in this form:

/cast [target=focustarget,harm][] SpellName

This means your lock with first try to attack your paladin's target if it's an enemy, otherwise it will attack your lock's target, allowing you to still solo the lock if necessary.

Then you just run your paladin up to a mob, press the key for the spell, and voila!

There are many other ways to do this, but this is (roughly) what I do with my paladin & shamans.