Another issue I ran into was that my Improved Mana Gems did not stack with the Mark of the War Prisoner "on use" so I had two different buttons to click - now that I've replaced the trinket, I have one macro which just allows me to go all out:
/use [button:1] Mana Sapphire
/cast [button:1,target=player] Combustion
/cast [button:1,target=player] Icy Veins
/cast [button:1] Mirror Image
/cast [button:2] Conjure Mana Gem
Since Mana Sapphire is first in the macro, it shows you how many charges you have left on the gem. It will quickly use your Mana Sapphire for Mana Surge, Combustion, Icy Veins, and Mirror Image (I used button:1 so it works only if you left click on the macro).
At the end, there's a Conjure Mana Gem spell if you right click (button:2) which will summon a new Mana Sapphire if you're out or refresh the charges on your Sapphire if you have used charges (which you should always do if you have two pieces of Tier 7).