2x8 timbers, about 3ft long with one end of each placed on top of the first rung of the ramp has allways worked for me, bar the occasional car where I've needed 8ft long ones with a brick under the middle and the ends on the second rung.
It used to be a major problem with getting an mot for me, as the local garage used to take the veiw of "if it scrapes going onto the ramp (4-poster), it fails". How I lol'dmao when they were told they had to spend £3k digging a recess into the concrete floor so the ramp was level with the rest of the mot area floor.