Yes, I've found that if the enemy marches close enough that they will often spot me - you need to time it right and use a good lure. Rolling hills or slight changes in elevation can help keep you hidden if you are behind a crest. Once you start moving you only have a short time while you get the bonus for attacking from a hidden position - I notice that if you hover your cursor over the hidden unit as it charges it will continue to keep saying "concealed" for a bit - I assume that's as long as your bonus lasts. Consequently I've learned not to hide my cavalry too far back in the woods or too far from where I hope to lure the enemy - I can waste their bonus as they stumble through the trees on the way out, or as they cross a big open area. It's all pretty tricky and requires a bit of luck.

Even if you don't get the hidden attacker bonus, you still have the advantage of popping up somewhere where the AI didn't expect you - it can often cause them to halt or reposition their troops, giving you other opportunities.

Besides your general, another good lure is mounted missiles - you can use a unit of horse archers to pull somebody out of formation, lead them past your hidden unit, then charge them from behind.