As priceless said, you don't want to give the yeast too high of an OG in the starter. You want them to focus on multiplying and creating strong offspring. If you get them too excited (high OG) you wind up with lower quality yeast. If you need more yeast than you can get with a moderate gravity starter (1.040), then you really need to perform multiple steps to increase the quantity, not attempt to use brute force and force feed them.