Cursed magic items refers to just that; cursed magic items. You then force the troll to "pick up" the item-usually by supernatural telekinesis.

Curse Weapon is also a spell that makes damage dealt by a weapon unhealable until a dispel magic is used. It allows no SR for the victim. It is unclear wether regeneration would turn that damage to nonlethal but in any case it will not heal. Your trolls, ofcourse, are immune to nonlethal so this is a moot point-but see below.

The main problem with your tactic is the 4th step. Grafts require XP so mass-creating them may cause problems. In addition, somebody strong enough (say, a wizard dragon-polymorphed into a wartroll or pit fiend) could tear the grafts out or sunder them. Finally, the average troll has a will base save of +3. Even with the best resistance gear, that's a will save of +12. You still have a higher than 5% chance of ruining the offspring.

A secondary problem lies with step 1. The only spell that makes mindless undead fertile is spark of life-but they stop being undead for the duration and the duration is too short anyway.