Menander I might've already done it IOTL, but I'm a bit rusty on Indo-Greek History.
Certainly, if you could manage to weaken the Indo-Scythians, and get a string of rulers the calibre of say, Demetrius Aniketos and Menander, who co-opt the remaining Mayuran administrative system, it'd be entirely possible for them to conquer the Indus River Valley, and hold it for a few centuries. Beyond that though, I honestly don't see them advancing very far, except by incorporating the Yuezhi or something, and then squandering the wealth of the silk road on campaigns in the south.