I'm not sure how the dispel mechanics changed for Pathfinder, but for D&D 3.5, the dispel bomb is another classic tool - bundle your explosive runes up, lob it like a grenade, and fire a dispel or erase spell at it. It relies on two potential sources for hang-ups off the top of my head, though:
1. You can intentionally flub your dispel roll. By default, dispelling your own spells is an automatic success for targeted dispels, and you get the choice for area dispels.
2. You can trigger all the explosive runes simultaneously. This one applies to some degree to the hand-delivered version ("oh, your minion only had time to read the first one before it exploded") as well, but this one either relies on either the use of an area dispel targeting all of the runes simultaneously (put them on separate sheets of paper and call them separate objects) or the runes chain-reacting. This one's the focus of a common house-rule fixing this in order to reduce the more ridiculous nature of runebombs in general.
Alternately, you don't need your minion to read it. Just tell them to try to non-magically erase disable the runes. With a DC of 28, if their Disable Device skill is low enough, they'll have no chance of success short of the common "auto-success on 20" houserule.
EDIT: Disable, not erase. The question of whether destroying the material a rune is written on or the writing of the rune will trigger the rune or simply cause it to fizzle is...ah, shall we say, a viable point for rules-lawyers.