I discovered this evil tactic almost by accident, hope it might come handy for someone.
I used to hire musketmen auxiliaries as a cheap filler in my North American army without any clear idea how to use them efficiently. Staying invisible while walking feature is not working very well against the AI: it still 'sees' the stealthy units somehow and sends cavalry to 'clean the field' right away.
Anyway, I had an army with 5 such 'fillers' in it. Not being sure how to use them in the battle in a meaningful manner I placed them on a side in a clear field, intending to attack the AI Iroquois position with my smaller force of Hessians instead.
Upon the battle start, it became clear that my main army was within the range of the Iroquois cannon. Just poking the AI's resolve, I sent an outfit of light cavalry towards their artillery position. Of course, the AI responded by sending lancers to intercept. Here comes the fun part. I ran my light cavalry back not towards the main army, but rather - towards (and through) the crouching musketmen in the meadow; sensing no threat from my main army, the AI followed in hot pursuit.
One salvo from all 5 musketmen units and bye, bye lancers with zero losses amongst the musketeers! rinse, repeat... That latter part, of course, would not work against a human player, but the AI seems to forget about what it does not see that very instant.
I guess, this tactic would work with any cheap 'hide anywhere' unit like Central European pandours, etc.