I use a wooden spacer (2x4) between the jack and the frame. You have to jack further to get the tire off the ground, but it is pretty stable. I use 2@ 20 ton bottle jacks, one before the first axle, one after the second axle on one side and try to spread out the frame load with a 2x4 so it is not so much of a single point of impact at the lift point.
Once you get the frame lifted and the weight off the axle on that side you could put a jack under the axle (with a spacer) to gently lift the tire off the ground. The weight of the trailer is on the frame and the 2@ bottle jacks at that point.
BE SURE TO USE JACK STANDS AS A SAFETY MEASURE incase anything goes wrong. NOT worth your linjury or your life!
Bob Weis