I usually just put quarters under the edge of the easel I want to tilt up. I also have a tilting neg stage for this purpose, which some enlargers have, and by combining easel tilt and neg tilt, you can use the Scheimpflug principle (that the neg plane, the focal plane, and the lens plane all meet in a line when they are not parallel), just like on a view camera to compensate for the change in the focal plane, when you want to correct distortion.
The effect you can achieve this way is equivalent to rear tilt on a view camera, meaning you can correct distortion in one visual plane, so it's good for something like a flat building facade, but isn't so useful for a group of rectangular structures at various distances from the lens.
Also, since you are focusing on the film and not the scene in three-dimensional space when enlarging, you don't have the control over the focal plane that you would with a view camera in the field, and if it's out of focus on the neg, it will be out of focus in the print.