I've thought about doing this myself and I would use coupler nuts. A coupler nut is like a really long nut, used to connect two threaded rods or bolts together. It's made as strong as regular nuts and bolts, and available at bolt and screw supply houses in a variety of sizes and lengths. Here's a photo:



My son's LT-A50's wheels mount onto studs. Nuts are then used to secure the wheel. I would use a coupler nut of the desired length and screw it onto the studs. This will give you a VERY strong extension. Then, instead of nuts, you'd use bolts through the wheel since the coupler nuts would change the gender from male to female.

Total parts: Three coupler nuts and three bolts per wheel. Add washers or use blue Loctite to prevent vibratory backoff.

 

WOW great idea, right now I'm having trouble fining them in a 5/16 x 18 3 inches long.

 

I posted a response yesterday but it vanished and never showed up here. I'll try one more time.

Using my son's LT-A50 as an example, what I'd do is buy coupler nuts and matching bolts. A coupler nut is like a "really long nut", an internally threaded tube. They're specifically designed to join threaded rods or bolts, are very strong, and are available in a variety of sizes and lengths at fastener shops (regular hardware stores may not have much of a selection, but specialty bolt and screw shops will have them).

Here's a picture of a coupler nut:



Currently his wheels are held onto the hubs by studs in the hubs. The wheel sits over the studs and the lugnuts screw onto them. Remove a wheel, screw the coupler nuts onto the studs, and then reinstall the wheel using new bolts that pass through the wheel and screw into the coupler nut.

Result: Wider wheelbase using very strong components that don't cost very much and are available almost anywhere. No irreversible changes, either - you can remove the extensions at any time and go back to stock whenever you like.

Hope this helps!