I've incorporated working on dance steps as part of my regular exercise regimen, which also includes the treadmill and some weights. So you can do all of it, and it makes the dance practice become part of a routine.
When I practice by myself, I make sure I am making the hand and arm movements that I would if I were with a partner. In other words, I push forward or pull back, or whatever triggers are normally needed, so they become ingrained as solidly as the footwork.
But it is like practicing in any other sport. Practice makes perfect, but it is still not quite the same as the real thing. Once the partner is your arms, it may not seem quite as easy to glide across the floor or do pivot turns, etc. But if you have it down solidly, the partner will find it easier to follow.
The bottom line, really, is that it is crazy not to practice.