Hi guys
I've been trying to avoid creating a new topic by sifting through the existing topics to add this to, but I couldn't find a directly related one.
I might as well be a bit too excited about this revelation and I suspect you folks out there may have already worked this out; so, dear admin please feel free to delete my topic if you find it inappropriate!
I've been using ProATC-X to create flight plans including SIDs and STARs and when you put your 727 in GPS mode the aircraft follows the exact waypoints and intersections including those of the SIDs and STARs beautifully.
It's interesting because with ProATC-X (I don't know of any other third party ATCs) the STAR is assigned in-flight and the GPS path immediately gets updated to reflect the STAR waypoints!
Now a couple of things to remember:
1. you won't have the luxury of VNAV, so your vertical navigation is up to yourself to manage; however the ATC will guide you with altitudes and restrictions are shown in a table just lower left of the screen in ProATC environment
2. you need to have updated your FSX NavAid database so that the ATC software (which is loaded with AIRAC database) can talk to your GPS and insert the waypoints; there are free DBs available to download but I'm unable to provide direct links as this is only my first post; anyhow I'm happy to share my source when I'm allowed (I'm sure many of you already know about them anyways)
3. by the same token you'll be able to fly ANY aircraft not equipped with a FMS using the above method

Sorry for sounding a bit excited about something this simple, and most specially with my first post.
Any ideas??

Thanks for that. It sounds like a really nice addition to flight simming. I'm not sure if I've ever heard about ProATC-X before, but I will have a look at it anyway.  ;)

You might try SimBrief. Download plan from it to be used in FSX. Will be able to use it in gps, not sure about Nav mode.
:) ;D

I just bought Pro-ATC and it does have some cool functions.  It is wonky as heck, though.   

And it is true that SimBrief can export a flight plan complete with SIDS and STARS in FSX/P3D format, which will allow you to use the GPS to fly the SID/STAR in the 727. 

I have created flights with the default FS Flight Planner (using user waypoints by draging the route line to a posintion acting like a SID and/or STAR), Flight Sim Commander 9, and Pro Flight Planner X (those last two provide proper SIDS and STARS).
Loading them using the default FS Flight Planner, and using the GPS nav mode achieve the same desire as the OP achieves with ProATC-X. ;)