Select victims from countries where submission to authority is ingrained at an early age.
Claim credit for influence that you did not have – “I am so pleased that your paper was accepted – I had to fight really hard for that one”. The beauty of this strategy resides in its unfalsifiability. It also works for letters of reference, especially if you have actually tried to prevent the candidate from obtaining the job.
The time-honoured approach is obligation through funding. You should “fund at the margin”: Providing the last 5% of funding to enable the obligatee to achieve their goal provides you with a 20:1 leverage on your investment.
Pick potential obligatees by keeping your ears open to troubles and laments. For example, a student whose scholarship is about to run out, but has almost finished their thesis, can be put into a position of life-time obligation for the small investment of three months stipend. A side condition will be co-authorship of all the papers arising from the previous work as well as the work to be done.
The above strategy can be combined with project management damage control techniques by offering the future obligatee the once in a lifetime opportunity to take over the lead on a project that is tanking badly. That way when the project does fail, you look clean, and the obligatee will mix shame and embarrassment in with the obligation to create a powerful toxic mix of emotional instability.