You'd still need engines and fuel onboard, or you couldn't circularize the orbit. The idea is more just get something out of the atmosphere with something that doesn't itself have to be dragged along for the ride, then do the rest of it once you don't have atmospheric drag and you aren't fighting directly against gravity anymore.

It's kind of the same as the idea of "what if the first stage was a big air-breathing plane that just, like, flew really high and really fast?" that keeps cropping up, just finding a way to make the first part of the process less absurdly expensive.

But no matter what you can't put something into orbit with a single input of velocity unless that was enough to remove it from the Earth's sphere of influence entirely, because you can't make the lowest point in an orbit higher than the point you're currently at.