I'm actually playing my warlock now, and my overall memory of Tsulong for my mage was madly Symbosis healing (as in the linked log) but let's see...
Personally I prefer a haste reforge, but it's not an exact science which is better. I'm also a normals raider this patch so perhaps my logs are better to compare?
The problem with using RoP is that he's correct; it's completely RNG where you will get the light beams, but he shouldn't panic. I've favoured an Incanter's Ward/Temporal Shield mix on fights with predictable damage; you can macro these to one button and it removes the requirement to stand still on your rune. Evo would be something to consider if he went full haste but personally I would not use it for mastery.
If he trains himself how to charge camp, he can very quickly move through Tsulong whilst using Arcane Explosion to keep his stacks. He Scorches far too infrequently to be a reliable source of Missile procs/mana regen but as the others have said this approach is being killed off so it's probably not worth learning; if you note my Tsuong log for instance, I have 3x as many missile casts. This doesn't really pertain to these logs but he should be using Cauterize; Invis is a waste of a GCD whilst Cauterize procs automatically and if he's smart he will IB once it's up. He should have a macro using Alter Time (normally with Arcane Power and any on-use. Mine also has my troll racial) which will reset his stacks and give him his powerful CDs. The Arcane Power glyph, for my part, shouldn't be used; you will get more predictable and frequent bursts with a 1.5 min cd, esp if dps is a problem.
Edit to add logs - I'm not a particularly good mage (my Tsulong log is especially poor) but I am in similar gear; http://www.worldoflogs.com/reports/x...?s=6805&e=7265 (didn't meter hump by multidot) / http://www.worldoflogs.com/reports/x...s=9650&e=10108
What he could do to help you guys on the adds is cast slow on one add, burn down another, and then switch back (presuming you assign your ranged to quarters)