Well it is possible, I did mine without. But that was when I was doing my front axle swap. Spring compressors are usually available for rent at auto parts stores. Or if your life isn't worth much, harbor freight sells a kit for $10.
The compressor will make it a lot easier, you should be able to get them on after unbolting the LCAs, shocks, and sway bar links. I think you might need to unhook the steering linkages, but I can't remember if it is necessary.
But If you unbolt the UCAs with the LCAs, shocks, and the links unhooked you should be able to get them on without compressors, keep in mind that my spacers were only 1.5, so you might have more complications than I did.