PC Affected by Touch of Evil. Has to kill ally

So I am currently playing Dragon's Demand and my Character - a Cyclopean Seer Oracle - got affected by the domain power feat Touch of Evil. Before dying an evil kobold caster cursed me into having to plan and attempt to murder my ally in 3 days. The DM told me not to pull my punches and do my best. I gave it some thought and came up with different ideas like pushing him into a trap or locking him in a room full of monsters but most of these arent really planned so I need some help thinking of a bigger scheme that is within the possibilities of a lvl 3 character and 2 days of preparation.

The adventuring companion I have to kill is a Human Tower Shield specialist who has always been upfront in most battles absorbing all maner of damage from traps, spells and the like. I have been healing him for the most part and assisting the rest of the group with utility and buff spells. I have also been known to wage into melee when necessary or really pissed (When we ran into a necromancer who raised 2 skeletons). My character is a follower of Pharasma and is very respectful of the dead and the newborn (No killing kobold babies). He is known for paying respects to the fallen by giving them a proper burial no matter their alignment or the fact that they were trying to stab us 2 minutes ago.

My ally has strengths:

• Lots of HP (Over 35 at lvl 3)
• Lots of Armor (Tower shield specialist + Heavy Armor)
• Very Good Fort and Reflex Saves

I believe I would lose in a 1v1 confrontation considering most of my spells are utility and support oriented. Even if I buffed up Id still have a hard time hitting his 23 AC

And weaknesseses:

• Low Will Save
• Low Touch AC
• Very big Armor check penalty (-13 or so)

So naturally I was thinking of a situation where his ACP would be his demise. Like drowning or falling in a pit. But most of these ideas seem very situational and improvised since I cant really plan to have a pit full of water in advance. Any ideas?