Here is a quick how-to on building turnbuckle mini jacks. These are surprisingly useful little things and can be made in minutes.
The version I built can be any length between 9.5" to 12".
Step 1: Materials
a turnbuckle, I used a 3/8" from Home Depot
two rubber stoppers, I got mine from a chemistry lab supplier
and a long bolt with the same threading as the turnbuckle, I used a 6" long 3/8" bolt
You'll also need the following tools: