There is no sculpt tool to go "straight from this point to this point". You can turn on Smooth Stroke in the stroke panel, which can help draw a straighter line behind your stroke by removing most of the jitter.
You can use masking to define the areas that your sculpting has effect. Using Box Mask will let you define a straight edge that your sculpting will stop at.
Another option is to define a black and white texture and use stencil brush mapping to place the edge where you want your sculpt to stop. With the texture brush mapping set to stencil, the image will appear overlaid in the 3dview. Use the right mouse button to move it around, hold Shift to scale and Ctrl to rotate live in the 3dview which can be easier than adjusting in the toolbar panel.
I made that using a simple blend texture using a colour ramp.