?? That's not genetic drift - genetic drift is the random sampling of genes that results from random mating in a parent population, leading, by chance, to unexpected gene frequencies. It can't be managed - it's a natural process. Obviously oak pollen isn't going to fertilise a daffodil... The problem may be where GM plants hybridise with wild relatives (which they do), have a higher fitness or some specific advantagous characteristics, and out-compete other wild plants creating an even more unnatural ecosystem. That's a real danger - and there's no way of definitely stopping it.