The way to be viable is to recognize that as a PC Free Spirit, you're going to be a cripple with 1 or 2 cheap tricks, and build around that. Don't try to fill the same role as a summoned spirit and don't try to have direct combat be your focus; even a crappy mage will be able to summon a spirit that can fight better than you, no matter what. Instead, decide what cheap trick you want to focus on, and put everything you can into being good at it.
An example is Voltron's Left Leg: Force 6 (55 bp), Edge 5 (30 BP), 65 bp on whatever, be a Possession free spirit, Aura Masking (3PP), Realistic Form (.5PP), extra Spirit Pact (1PP), do something amusing with the last .5PP, then the spirit pacts Friendship (pretty much required) and Drain. Have your bestest buddy be playing a foci-happy Possession tradition mage who picks up Channeling ASAP, make the Drain Resistance pact with him, then hang out inside him 24/7. This turns the two of you into a Voltron-esque supermage, but with Realistic Form and Aura Masking you just look like a mundane. You can also hide active foci and spells with Aura Masking which makes it even crazier. With your next PP, get the spirit pact Magic so the two of you can go super saiyan once a day, and then I think the next most hilarious thing is to pick up Power Pact and some power that combines in an amusing fashion with a different PCs abilities, like giving an unarmed combat adept Elemental Aura or giving a pornomancer Fear or Influence.