Funny, I would rather complain about being able to level past 50, while you're trying to get access to Heavensward, instead of the leveling of second classes being tedious. Except for all the DPS classes maybe. I save as many quests and leves as possible for the time I decide to level a DPS class.
I'd say it's all about patience. Make use of the rested XP and the daily bonuses with your second class. Then level your main, enjoy your time in the Gold Saucer or do anything else, while you wait for the bonuses to reset. Sure, overall you're probably going to need longer, but it's way more efficient and wont feel like such a chore.