With a turboprop there should be a power lever setting that gives drag equivalent to that present when the engine is shut-down with a fully feathered prop. this technique is used quite a lot in flight test when it is necessary to test the asymmetric performance and handling of the aircraft but without the risk associated with having an engine shut-down. As previous posters have stated, it is nice to know an engine is available quickly if needed!
As for identifying the best power lever setting for simulated asymmetric flight, it is fairly easy to do if you have rudder angle and sideslip gauges available, but slightly harder on an un-instrumented aircraft. One technique that would be worth trying is to establish the aircraft in straight and level flight with one engine shut-down and feathered, then note the speed, rudder and aileron trim settings used, and also the angle of bank. Then repeat with that engine operating and see what power lever setting will give you the same combination of speed, bank angle, rudder and aileron trim in order to maintain straight and level flight. A similar exercise could be done in the climb if required, maintaining speed and rate of climb as well as bank angle and trim settings.
If you decide to try either of the above I would caution: 1) make sure you have enough height to recover and restart the shut-down engine if it is needed in a hurry, 2) be very careful with respect to VMCA, your stall speed and any sideslip or rudder related limits, 3) get a radar service to help with you traffic awareness, 4) know what you will do if the good engine quits, if you come close to a limit (e.g sideslip, speed). I'm sure other regulars on this forum could probably add more things to consider as well. And to be frank, before trying any of the above it would probably be worth a chat with the aircraft manufacturer, because they will probably have established the necessary power setting during early flight testing and certification anyway!