It shouldn't be too hard to retro-fit reverse to your sled. You'd need a chaincase with reverse and the associated controls for it; looks like the 500 classic would be one model you could get it from, and I see a couple on eBay (not the cheapest source). That said, in most situations where I've been stuck, reverse wouldn't have helped. It's a great thing to have for unloading and handling tight spots on the trail, but once you've buried the track in deep snow, it's probably not going to make a difference.
As for not getting stuck, it's largely a matter of experience, and experience comes from getting stuck! :face-icon-small-ton Partly kidding, but it's hard to give any exact techniques for how to judge the snow, terrain, and momentum. With a short track sled, you're always going to be fairly limited once you get over a foot or so of soft snow, so keep that in mind. You might just find that your sled isn't a good choice for the style of riding you really enjoy. Anyway, in tight areas, I try to read the terrain and work from high spot to high spot. You want to keep enough momentum to where you'd get at least halfway up the next rise just coasting, fight to initially track a little more up the slope from where you want to go, and pick a secondary downhill turnout in case you can't hold what you planned. Unfortunately, even with a little more sled than yours, I find the only way I really guarantee not getting stuck when the snow is good is to stay on the trail. And that's no fun!