OT...your training has missed some important steps... groundspeed is the worst to advise. Just think about a nice autumn or spring day with winds of about 50 kn westerly directions above FL 100 and about zero wind at FL 80 with about 30 to 40 knots easterly on the ground...now what do you expect us to do...
What you want is to have all the flying targets on your screen lining up at the same speed. This works only if all use IAS...
I am not aware of any autopilot which can be hooked up to groundspeed...maybe the newest digital gadgets have this feature, I don't know. So with GS instructions you will create some mess because everyone will be more than busy with constantly adjusting power setting and aircraft configuration to match the demands...the only answer you will get is...unable to comply due to safety reasons...