Is it just putting two needle valves "in a line," that is, the fuel tank to the remote needle and then the remote needle to the engine mounted needle (set wide open)?
Yes, exactly. I would not want to put the remote needle too far from the existing needle, just enough to mount it facing fore/aft & mount it in a convienient position. Yes any brand would do (except Fox! [:'(]) but don't use one designed for a .40 on a 45cc engine as the holes for the fuel flow would obviously be too small.
For what it's worth I have never used one, it just struck me as a neat idea designed by someone else..
What I usually do is like suggested before, solder a cap head (allen head) from a bolt to the end of the existing needle & adjust it with a long allen key.
Like camdyson said, you really should not have to tweak a needle too much anyway once the engine is tuned. If you do it's usually a sign of some other problem, usually crap in the needle valve. I don't want to get into that most stupid of all arguments (should I use a fuel filter or not, the answer should be obvious) but with a proper filter fitted just before the needle valve this should never happen. - John.