Just found out the old reliability equation:
Net Reliability =1 - (1-r1)*(1-r2)*(1-r3)........
So by casting 90 Ghoul Glyphs, there's a 99.0112 % likelihood that the affected creature will roll a 1. That's waaay too many ghoul glyphs. Assuming 6 2nd level spells/day, that's 15 days, doable, but I think we can do better.
Assuming we can put pieces of paper with Explosive runes cast on them on the square we want to summon the creature, and that we can choose to fail a dispel magic check against the runes, that would seem to me since it's no save, that we can cast 10 runes for approximately 210 damage with a near guarantee of success.