at anything other than very light weights
At least one 737 operator in RSA had this situation some years ago when I was working over there but they weren't training for it. Led to some interesting eye-opening in the sim when I starting introducing the problem in free time.
The company therefore removed the VMCg tables from the QRH as we do not need it anymore.
Don't like that. So your company doesn't have any interest in the interplay of Vmcg and crosswind ?
VMCg is only fixed for a thrust setting, since thrust settings are not fixed though it is another value that can be played with.
Now that's just plain dangerous thinking. Vmcg is fixed for the rated thrust setting. When you flex (I'm presuming that you are so referring) the Vmcg stays the same. When you derate, the rated thrust and Vmcg reduce. Beyond that you have no option to play with the numbers.
just assume a heavier weight by going up the column until your speeds were no longer in the shaded area and then select those speeds provided you weren't limited in other areas such as field length.
For a typical RTOW chart (I presume this is what you are looking at), and in the absence of any specific prohibition, that should do the trick. Functionally all you are doing is generating an overspeed takeoff. Regarding field length, you will be covered by the weight delta.