first of all, just KICK THE SHIFTER!!

you have to mean it when you up shift!!
if you search the forum you can find a post i had written maybe 2 years ago about how you should set up your shifter so that it would minimize the chances you could get a false N... after i fixed the possition of mine i had a false N only 3-4 times and i was always to blame for not making a good gear change...
you can also set your oem shifter as reverse so that you can check if the false N you get are due to the fact that you dont change the gears as you should!In reverse its easy to just kick the shifter down, so if you push the shifter all the way down and you still get a false N, then i guess you have a problem, either big or small!

...i bet you wont get any though...
ttpete is right too...you should bleed the system both at the slave cylinder and the master...