The training ground Peak boost event works great at giving extra peak XP during the current event. It should be easy to do the same with Goblin Mines for a week or two at a time. Certain restrictions would need to apply. The boost should require that the character run the event solo and be on a class combo that qualifies for peak (100/100). Otherwise it gives the same xp as normal, even on peak characters.
If the game mechanics allow, XP and TP buffs from runes, wings, guild buildings, and potions should be deactivated while in the instance. Furniture buffs, maybe or maybe not.