[Gimp-user] Zoom layers independently, or overlay an image at different resolution?

[Erika quinn <lovelace crossproduct net>]

I'm doing some low-resolution spritework for a project of mine, and I'd 
really like to be able to work by doing the pixels on-top of a much 
higher resolution sketch of the character. (Basically, a sort of 
Prince-of-Persia-esque rotoscoping, but with hand-drawn artwork)

I've managed to accomplish this to a limited extent by making a second 
layer, creating a very large square brush, and a wide grid with large 
snap extent, but this is kind of inelegant, and it limits me strictly to 
working a pixel at a time.

Is there any better way of accomplishing what I want? Has anyone else 
ever even wanted to do something like this? (I've had zero luck googling 
the problem because I can't even think of a concise way to phrase it)