Best way to manipulate a large enemy group through its leader

I'm trying to come up with the best way to somewhat take control of an enemy force by taking control of their leader. At the moment, the character trying to do this is a mid-level summoner with a decent UMD and an eidolon with an even higher UMD.

I currently have 2 thoughts on this, but there are some rules questions I'm unsure of.

1) The simple way: Dominate person. However, what would the DC be on a dominate person scroll? I suspect it would only be 10+ spell level and not add any ability score bonus? that's pretty easy for a level 7-8 enemy to ignore. What other spells/items can a level 7-10 summoner use to lower saves to make this viable? Would several low level witch followers (leadership) work too?

2) the complex way:
Get the leader and kill them.
Cast gentle repose on the corpse. Can permanency be used with gentle repose?
Cast create undead from a scroll (UMD 31 twice for ability score and scroll). Turn the enemy leader into a zombie lord. This only works if there is a way to use gentle repose permanently. Would it be possible to create a wondrous item (cohort is a crafter) to create a gentle repose effect permanently? How much would this cost?
Also in that vein, if the enemy leader has a charisma of 18, Create undead can turn it into a ghoul with the Civilized undead feat.

Any other methods using a combination of items and spells as opposed to story mechanisms (blackmail, diplomacy, etc)?

magic jar?

Charm person and diplomacy?

Suggestion that he take advice from you.

magic jar?

I hadn't thought about magic jar, its actually a summoner spell so it could actually have a decent DC. It'd only last for 9 hours, but that should be enough time to sow enough chaos in the enemy ranks.

I don't think charm person would work. While the character has a high diplomacy skill, a charmed person would still only treat you as a friend. It might help make diplomacy easier for a short period of time, but I'm not sure it would cause much harm to the enemy without providing numerous saves.

Suggestion might work, but again the problem arises as with dominate: low save DCs.

Give them accurate, useful information, ingratiate your way into the group as a turncoat, and then steer him in the wrong direction, or just kill him and take over.