I'm afraid that no, Elementals were left in a rather primitive state customization-wise. They have a standard sfx attack strength, which cannot be buffed by player affixes (or the Affliction expertise, since that too refers to the player's own sfx attack strengths). The only one which has a customizable sfx attack strength is the Spectral, which gets a phase attack bonus through its skill level.
You *can* indirectly improve their chances to apply sfx by using Elemental Drain to lower the enemy's sfx defenses, but I believe that's pretty much all you can do.
If you are into modding (or another player is), it'd be possible to create a passive skill for this purpose like 2038 did in Master of the Arcane. You'd need to make a blank skill, and have all Elementals get an sfx bonus based on that skill's level. Steam's Summoning Empowerment skill, which buffs Demons' sfx defenses, should serve as a point of reference there.
I suppose making such affixes for players to wear wouldn't be impossible either, but I'm afraid I don't know how that should look.
