You can do the same thing that is done on the youth machines I think. The throttle stop is nothing more than a hole in the throttle housing on the handlebar with a screw that limits how far the throttle is allowed to open. Then a jam nut to lock it in place. If you can, go to a dealership and have them show you the throttle stop on any of the youth machines. I think it would be fairly simple to do.
I will try to remember to post a photo from the Sportsman 90 I have for the grandkids.
Mine: 2018 Sportsman 850SP - 26" Bear Claw HTRs on OEM steel wheels(I really don't like the Aluminum ones)
Polaris Hand warmers, Mirrors.
Hers: 2019 Sportsman 450. 26" Bear Claw HTRs on Moose 427X Wheels.
2007 Sportsman 500 EFI, Polaris Winch, 25" Bear Claws QSC Clutch Kit, Hand Warmers
2001 Magnum 325 MOSE 12" rear wheel conversion. 25" Sedona Coyote tires
2017 Polaris Ranger 1000XP - Roof and front glass
2018 Kawasaki KLR650
2001 Magnum 325 Warn winch and Moose 60" plow-Sent to Daughter and Son-In-Law since his blew up
SOLD 2004 Sportsman 600 Twin