That would be a very tall order....Do not think it is possible...They should sit you right away because you are going at first seating...But the meal takes about an hour (maybe more) and you still have to travel back to the MK and get through security/gates...
If you want to try I would suggest NOT taking the monorail back to the MK...Walk from the CR is faster because the monorail makes three others stops before arriving at the MK if you are coming from the CR...
I am thinking that the CG is expensive and an experience you should enjoy, not rush through...Save it for a night you can stay and enjoy if possible...
Maybe pick a place that is open for lunch through dinner so you can eat earlier...Such as the Whispering Canyon Cafe at the Wilderness Lodge, Kona Cafe at the Poly, the Grand Floridian Cafe, the Wave at the CR, or the Trails End Buffet at Fort Wilderness...We like the lunch menu at the WCC!