Hrm... I suppose under those conditions I'd take the 50%/DT or 75%/DT, burn off some internal until I had what I wanted then switch to the DT, so that if/when I had to drop the DT prematurely I wasn't heavier than I wanted to be.
I know, not the best solution... Although I think if they ever fix the 152 properly you won't need to worry about fuel state nearly as much.