Changing Source Port For Nmap Idle Scan

[SecureHacK <debonaire52 () hotmail com>]

Hello  I have a quick question I have been experimenting with idle scanning and I have read the paper on it and I have 
an understanding of what goes on during the process I am also an avid nmap user.What I am trying to figure out is is 
there anyway to change the port to use during the idle scan by default it's port 80 so using the -g option it should 
change the source port to whatever I want I have used this option but it still only uses port 80 is this changeable? 
For example find a machine with port 139 open could we change our source port to 139 and use that?

                                        Cheers