No way to select a random waypoint in FS9 Flight Planner. You can with a couple of payware addons....FS Navigator or Flight Sim Commander, I believe. (
you can download a 20 session evaluation of FSNavigator here)
If you still have FSX installed there is a freeware utility that will convert FSX .pln files to FS9.
Filename: flightplanconvert.zip
License: Freeware
Added: 3rd March 2007
Downloads: 1000
Author: Gerhard Berendt
Size: 70kb
Dave
The reason why I purchased FS Navigator, many, many Moons ago.
(For FS 2000, FS 2002, and FS 2004)....
...not available for FSX.... one of the many reasons why I don't use FSX!...

!
Without it for my daily Flight Planning, I would have abandoned MS Flight Sims long ago!...

...!
...you can select any Waypoint you wish, along your route...

...!
Paul...G-BPLF...FS 2004...FS Navigator.*.. 8-)...!
* The full version is no longer available.
Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.