I've always used a light stand under the front bed. With so many strobists around, light stands are cheap and good enough to support the front extended bed.

Or find a used car undercarriage jack, the one that screws.

When I worked in the studios, they used 2 cement cans and a stick on the sides of the front standard, and a 1x2 longway and come A clamps. This was the days of shooting LF for magazines and print.