You just have to use the right combination of Gro+ and Reducto. Gro+ always adds .5" width regardless of size but adds less length the longer it already is. This means that the more you add, especially to ridiculous levels, the wider it becomes relative to length. Reducto, on the other hand, always takes around a third from both length and width. Ergo, make it ludicrously huge with Gro+, then shrink it with Reducto, and you'll end up with a fat schlong.