I had the factory bags and then switched to H&B bags
The factory spacer is just a tubular bar which has rubber feet on either end... (as you can see in the pics above)
The factory bar has adjustments for 'spread' and it mounts on the
inside of the mudguard
the H&B bar is a piece of flat stock that runs
outside the mudguard and
under (not below) the tag mount plate
You could easily make a flat bar with mounting holes to run under the plate like the H&B bar... then bend slightly forward once it clears the mudguard to hit the bags...
put a 90degree bend on each end and drill a hole for something like this:
http://www.surpluscenter.com/Miscellaneous/Other-Miscellaneous/CYLINDRICAL-RUBBER-ISOLATION-BUMPER-MOUNT-1-4038.axdthis would deff be a "measure twice; cut once" proposition... but the upper bag mounts alow enough 'swing' that it wouldn't have to be dead-on-balls accurate
The other thing to consider is the bags interfering with the exhaust can!
Part of the factory bag mounting is a short dogbone link to lower the can aprox 1.5" to clear the LH bag
My bike has a Staintune, so I did not need it to clear the factory bags or the H&B... But if you have a stock can you may need to drop it a bit.
***dropping the can will also lower the centerstand in it's retracted position... something to be aware of***
As you prob know, the centerstand has terrible cornering clerance in the first place!
You can ameliorate this a bit by trimming down the rubber bumper stop on the centerstand to gain back a little clerance
Hope that helps.. I can take pics of the H&B setup if you think that would be helpful