Mode 7 effects with height differences?

Usualy, Mode 7 (it shureley is called something else, but you know what i mean) is used as a flat ground (Mario Cart, Street racer) but some games have managed to make hills in a mode 7 engine. There is a snes game that uses it, and Moto Gp and GT2 for GBA also uses this. It uses Mode 7 but it has slopes, hills and height differences in the landscape. How is this made? Someone said that it was made by warping the screen somehow. Anyone who knows this?
"Mode 7" on SNES and GBA is a rotated and scaled plane, where the scaling parameter is changed on each scanline thus creating a perspective effect. You can stretch part of the screen to screate a slope/hill effect, you just have to calculate the parameters. However, you're still limited to a plane, ie. you can't make a hill rise in the center of the screen with flat ground on both sides.
You can, never the less, put a diferent scaling parameter for every screen scanline... You can use this in some engenious manner to create "slopes", I suppose, but this seems way far fetched, and the result would look like some sort of crummy Voxel engine.