Backbows, swimmers and the like

What exercises would you recommend that would help me get better at all those exercises that you do on your stomach - backbows, swimmers, and such? I can barely lift my arms off the ground in that position, so the version of swimmers where you keep your arms hovering and lift them up and down is not possible, because I only have one "setting" up (maybe 5 cm off the ground) :-D Similarly with the version of backbows where you're supposed to move your arms and legs from left to right, I kind of do it by waving my arms slowly, as my chest refuses to lift up from the ground.

I've been working out with FB for close to a year, these kind of exercises appear in workouts and programs often enough that I would have thought I'd make some progress by now like I have done with other types of exercises, but I seem to be staying on the same level with those :-/