Be careful about trying to control the chain whip at any distance from either sprocket. As the chain runs through it's various ranges of speed, the peak amplitude of harmonics in the lash will move from one area of the length....to another. Trying to catch that particular "falling knife" could be kind of like....trying to catch a falling knife! (humor...
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I have messed with rollers, idler sprockets, etc. in various applications. They can work good if you are willing to operate at a pretty much fixed speed.
That is why they completely disappeared in every manufacturers cam chain systems, many years ago (and were replaced by sliders). I even had to ditch the idler sprocket and go to a shortened cam-chain type slide in my "replica 1915 Smith Motor Wheel" project...and that thing has very short runs (the entire engine, clutch, gear reduction, freewheel, sprocket sets....all fits inside a 20" bicycle rim).
When we went to timing belts, we quickly learned that the tension and guide idlers had to be kept really close to load or direction change points. Trying to work in the middle of a run broke all kinds of interesting stuff.
Simpler is better. Just give the slack run a clean, smoothed exit and replace chains when in doubt. You will not need more than about 10" of slider to let that chain get settled into the idea of heading for the rear wheel.
JimL