You don't necessarily need Wifi, as just after flashing you have the network connection over USB (rndis) available. You may be able to ssh in over that and run some commands over ssh to do what you want...
Is there is a simple solution to send (and execute) a custom script to the edison just after flashing to set repetitive setting/tasks on the board.
Of course, this step has to be done before wifi connection and the use of the command configure_edison
A solution could be to make a Arduino sketch to fix some parameters with the use of the system function.
Any ideas ?
is it a one time task? Then why not just updating via serial or USB rndis? Otherwise, if it's for multiple boards:
if you build your own image you do have post_install scripts executed.