I've done it both ways. When I built my 3-tier I used flex tubing to each burner. For one burner (center one in the pic) I used the hose that came with my turkey fryer. You can't remove this orafice - it's a single fitting. The other two were connected with flex hoses I bought locally. The fittings on the tubing were flared on one side that attached right to the flared burner orafice. The other side had pipe threads that I threaded into the ball valve.
On my single tier, I used black pipe for the plumbing. I used the pipe threaded orafices
from morebeer. Without them, I don't think this is possible. I connect the tank and regulator with a flex hose to a flared fitting on the end of my stand plumbing. I prefer the hard plumbing. I also helped someone hard plumb a 3-tier and it looks much cleaner IMO.
I've got some other pics here
if you want to take a look. I probably didn't explain everything well, but I'll answer any questions I can.