There are two versions of this trick, I do version 2 regularly, I've never done version 1 before my current game. I don't think they are too gamey because movement is so hard to control in this game, but they are probably not WAD.
Version 1: In my current game (if you are not Straight Arrow, you can see the situation in the aar, here), Beauregard was in Manassas with about 30,000, but I had flanked him and put my main army under McDowell in Culpepper. I had two divisions nearby under Foster and sent them towards Manasses on a trip that would take 17 days. I left Falmouth open-ish, so that Beauregard would have the option to flee (see: Art of War). If he did, Foster would arrive in Manasses the next turn on day two. If he didn't, I'd cancel the move (see version 2). Beauregard obliged and moved into Falmouth. So I let Foster finish his trip. Beauregard's move was a feint, trying to get me to attack Manassas, which he intended to move back into immediately. Even though the Confederacy has an advantage of higher MC and strategic, Foster had an unseen head start (replay doesn't work for me, I don't know if Straight Arrow could see the start of the move) and got into Manassas first. I hadn't thought it might be a feint until the last minute, but I did ask Straight Arrow, and when he sent the turn back, he said it was. I haven't opened the turn yet and don't know what happened next, but presumably Foster and Beauregard had a fight.
Version 2: Moving from Tuscon into the main map can be tough in the winter/mud, a trip in these conditions even with full cohesion might take 32 days (or even more than 45 since the troops can get so tired and an initial long estimate can get longer) or something; but very fast in clear weather, taking 17. It is often best when you have a depot in Tuscon to wait for the weather to clear before moving east. In such a case, on one turn, tell your stack to make the (32+ day) trip. During that turn it gets 15 days closer to its goal. On the next turn, cancel the move, but don't do anything else (so don't move your stack into the structure if you are out of it and don't move it out if you are "in" it, and don't add anything to or remove anything from the stack - although you can change the disposition). Now on the next turn when weather is good (it could be turn 3 if you are lucky), order the move again. Now your move will take two days and you will lose barely any cohesion (since you've only been marching two days, not 17).
I didn't realize how sneaky this can be until just now, hearing that it worked in Manasses (again, I haven't loaded the turn and am not sure how well it worked). I think Europa Universalis now has it so that when you start a move, after a certain amount of time you cannot undo it without reaching your destination first. What do you think? Is this gamey?
I do some other gamey things, but try to limit myself, although I am somewhat personally ashamed of some tricks I do (for instance, I'm embarrassed that I use redeploy for generals and for support units like HQs and Hospitals, but I still do it, and I am not embarrassed to use river movement because I only use it behind enemy lines - although in this game I did lose a garrison militia moving to Island 10 to an enemy naval stack since the Island is at the front line).