I have an old globe at home that has bumps for mountains - clearly not to scale of the size of the earth, and I don't know how accurate it is anyway (the Rockies feel higher than the Appalachians, but I don't know if each individual mountain is represented or if it's just a regional-type effect). Anyway, you could always do what my globe does - just pick a different scale for elevations than you do for overland distances. Alternatively, rather than doing the whole earth you could do a small enough region that the elevations can be seen in scale with distances.