That's what I did to my mac mini. I don't know the "year" name of it, but its the original style case, 9400m model mac mini. I took out the internal drives and and cut a hole in the back. Then I ran two extension cables out the back which plug into a large pc case that has two 3.5" hard drives. It also has a bunch of drives that are on firewire bridge boards, which also plug into the mini. Unfortunately it's not quite as reliable as I would have hoped. Every few months or so, it locks up solid for no reason. It's too bad there isn't a better solution for me.
But I don't even use my wifi, I'd love to replace it with more sata instead of firewire. Would that work in my mini? a card that supports sata with port multiplication would mean bye bye firewire. Not that firewire is bad but, for this sort of thing, direct "internal" connections are always best.