If the airway is too far away to accurately determine which leg you are going to intercept, why would you let the G1000 pick the leg you are going to intercept?
You know best what you want and, as you say, ATC may change your heading anyway.
So you shouldn't intercept automatically until you are fairly sure where you are intercepting. Instead you remain in HDG mode which gives you full control and makes it easy when ATC instructs you to change heading. Then when you are a couple of miles from intercepting you select the leg and let the G1000 do the magic if you want to.
Automation is there to relieve you from difficult or boring tasks. If you find that you spend a lot of time programming your FMS, it may be better to reduce the level of automation and spend the extra time on situational awareness.
I recommend watching this America Airlines training video on automation dependency (a.k.a. "Children of the magenta line"). It addresses the FMS / autoflight dependecies for airline pilots. The video is over 15 years old and by now similar automation systems have entered the cockpits of small aircraft. Although some aspects of the video address a multicrew environment, the main points are equally valid for G1000 equipped single crew / single engine propeller aircraft.