OK, this is the simple explanation. I warn you though that it is complicated to work out in reality.
Simply put you create one taxiway from the front of the parking spot to the the runway entry point. Then you create a taxiway from the exit point(s) of the runway to the back of the parking spot.
Things that complicate it.
A. You have to plumb for each parking spot. You might get lucky and have a row of parking that will all join up into one taxiway.
B. The two pathways have to be completely separate. Any join point WILL cause you trouble.
C. You will have to be very cunning to create the taxiway markings that you want, and only one set.
D. Two pathways WILL cause you afcad difficulties. You just have to solve them when they occur, even if you just use taxiway out and apron route back.
E. You have to do this for both ends of the runway.
F. More than one runway and more than likely you will be f**ked.
G. Finally, despite what you want the aircraft will always take the shortest route to the runway entry point. Therefore you can't have the runway entry point be an exit point as well. Else the aircraft will reverse out, if there are parked facing away from the runway.
H. If the runway only has entry points and no exit only points then you are f**ked.
This should get you started.
