I've seen some use several large steel hose clamps to compress the springs. Not the safest probably, but If you used enough of them I would trust it.. using those you can probably compress the spring enough to disconnect the ball joint, then drop the spring out the bottom, perhaps it may need some prying with a pry bar but I'd bet it would come out.
You could also try compressing them with several ratchet straps, then when you get some compression on them, before you disconnect the lower control arm ball joint, add some mechanics wire on them as a safety.
I never had any luck with spring compressors on foxbody mustangs. Many just don't fit. The rear springs are not nearly as hard to change but still require some caution.
Maybe the hose clamps and the 2x4s from engine cradle to ceiling joists would be best? It's harder with no engine in for sure as you know.
Good luck and be safe. If you try something and it seems too sketchy, stop and reevaluate.
Honestly, regardless of how careful you are, doing coil spring work always has a degree of sketchiness to it. You just have to be as safe as you can and really pay attention to things...(and where your hands, face. Arms and legs are located at all times)