Possible?

Would you have to bind them somehow (true name) first?

i don't know if the rules specifically forbid it or not, but as far as i can remember, you should not be able to.

I seem to recall that being possible in SR3 or 2 if you had the free spirit's formula...

However, in SR4 that's not an explicit option.

I hope not.

No. Invoking metamagic may only be used on the basic spirit types the magician's tradition can normally conjure. What this means is that Invoking might even work on free spirits, but metahumans have yet to figure out how to do it.

I really don't want Free Great Form Earth spirits running around causing Quakes and making Life Pacts. That's freakin' scary...