Don't know how you'd do it on a FI model. Carbed one, all you need is something to crimp on the throttle cable where the cable itself goes into the sleeve, you want to limit the travel.
Depending on the model if the throttle itself has a stop, then just loosen/lengthn the throttle cable adjustment at the carb so that at full push of the throttle, it only open the blade as much as you want it.
M&P-10 - Kel-Tec RFB - AAC Cyclone
ATN OTS 336-50mm 9hz Thermal Monocular
ATN NVM14 NV Monocular