has anybody flown jetways?

If you're up at those levels, you'll probably be using Waypoints, that connect the Jetways that you're referring to.

These Waypoints are fictitious points, although they generally relate to a meeting point between 2 VOR radials .... (I don't know if I explained that too well).

Anyway... most planes that are capable and legal to be flying Jetways will have a Flight Management Computer (FMC) that will navigate the Jetways without any trouble.

If you were flying something like a 727 without a FMC, you'd most likely file a Navaid plan that uses VORs and NDBs, rather than Waypoints.

In the world of FS ... the answer to your question is that you would fly the "High Altitude" option within the FS Planner.

If you have an FMS or other navigational computer on board your aircraft, you are legally able to fly from one waypoint to the next. If may cut down on your flight time be doing this as well.

The FAA regulations do not prohibit flying direct via GPS at altitudes over 18,000 feet. They only state that you must be under ATC radar control. Since you must be instrument rated and on an instrument flight plan when you are flying over 18,000 feet you already have the requirement satisfied.

There are not nearly enough jet airways to cover every possible flight that pilots want to fly. At your departure you would have to fly toward a jetway, using a path that is not an airway. Then you would have leave the airway to fly toward your desired airport, using a path that is not an airway. So you would be using the GPS for navigation anyway.