I have the same problem losing both the temporary hypnagogic visualization and lucid dreams, rare as the latter even are for me: it's so easy to do something silly, like pay too much attention to it or get excited about it, and BAM, it's been destroyed.

I did have one occasion where the hypnagogic thing had mild success when I tried to imagine something non-stationary, in this case sort of watching landscape go by as if I were in a car watching it through gaps between concrete pillars in a bridge railing.