If that were possible, that is, if you could take an x-coordinate, and find the private key $k$ such that $kG$ has that x-coordinate, well, you've just solved the discrete log problem. If you can do that, you've just shown that the curve is insecure.
If you're thinking "I'm not specifying the y-coordinate; doesn't this make it easier than the discrete log problem", actually, no it doesn't. There are at most two points that have a specific x-coordinate, and those two points are inverses of each other. If you known the discrete log of one of the points, you immediately know the discrete log of the other.
As for choosing the most significant digits of the coordinate, I don't know of any easier way that brute force (that is, start at an arbitrary place $kG$ and test $kG, (k+1)G, (k+2)G, ...$ until you stumble across a point that meets the condition.