You don't need a benefactor to practice that type of metta; you just need someone who is dear to you; it just shouldn't be someone you could potentially desire sexually, or whom you are partial towards, like your children.
The stages, according to the Visuddhimagga are as follows:
- cultivate metta towards yourself (useless, but a good example)
- cultivate metta towards someone you hold dear
- cultivate metta towards a neutral party
- cultivate metta towards someone you dislike (optional, only for those who have such a person)
Having someone dear to you seems important, as there is no advice given for what to do if such a person does not exist. Ostensibly, you could skip that step and try to immediately cultivate metta towards a neutral party, but the dear one is useful for returning to when difficulty arises with the other objects.
Alternatively, you could try cultivating metta in order of proximity; may I be happy, may all beings in this room be happy, this building, this city, this country, this world, the universe. Also, by direction; may all beings to the East be happy, etc. Or finally, by class: may all women be happy, men, animals, angels, etc.
Mahasi Sayadaw has a detailed exposition of the four brahmaviharas that is both practical and informative:
As he says,
"Mettā can also be developed towards any other person deserving of affection and respect, if not towards your teacher, grand-parents, mother, father and so on."