Rumor has it that Relentless Earthstorm Diamond is fixed for melee classes in 2.2.2. While this is a good thing for Tonberry, it looks like it will probably not be fixed to work for casters. (It is entirely possible that since it's a +Agi gem, it was never intended to work for casters and the loophole that allowed casters to use it was introduced solely to allow Arcane Shot to work with the gem.)
I've worked out how I can use Mystical Skyfire Diamond but it depends on a single drop from Gruul.
Currently, my gemmed raiding gear pieces are:
Between this and my other gear, I have a hit rating of 171.
I also have a Depleted Cloth Bracers waiting for me to turn it into Crystalweave Bracers. (Not like Apexis Shards are rare or anything.)
If Gruul drops Leggings of the Fallen Hero (and I win it), that will give me Legwraps of the Aldor for my leg slot. I could then make these changes:
This will then give me more blue gems than yellow, satisying the requirements for Mystical Skyfire Diamond.
If you're wondering why I put the two Glowing Nightseyes in the boots, it's to ensure that the meta gem will function in my non-raiding gear. My non-raiding gear would replace the non-socketed Mantle of the Elven Kings with Pauldrons of the Aldor and Legwraps of the Aldor with Trial-Fire Trousers. If I gem Pauldrons of the Aldor with Radiant Chrysoprase (at least until I get Polished Chrysoprase) and Glowing Nightseye, that will still let me gem the Trial-Fire Trousers with three Potent Noble Topazs and keep the meta gem's conditions fulfilled.
Edit: By accident, I originally listed Vivid Chrysoprase in place of Polished Chrysoprase. For level 72 mobs, having a +spell hit gem is silly and I apologize for the mistake.