Depends on your guild really. I would go as far as to say 55% reuse + 15 cast/reuse + 10 cb on yourself > 10 cb for a mage dps (who is already capped on cast/recov/reuse for most fights). So if your guild runs 2 mage groups, each troub can jcap a scout dps and themselves. If your mage group happens to have a third scout dps in it jcap them instead of whichever scout is getting RoA.
If your guild only runs 1 mage group/1 troub then you're outta luck.