How do I internet share on stock rom?

[master4g]

I have a Diamond on sprint and I use internet sharing by just plugging in the usb and the menu pops up with options (activsync, hard drive, internet share) and I choose internet share and it works no problem.

I got a HTC snap on sprint for my dad. He will probably never use the internet but he has a data plan (family plan) and I want to set him up so when his internet goes down (often) he can take advantage of his phones internet for once.

However, on his stock Snap, when i open "internet sharing" i get an error pretty much saying wrong login/password...I dont have this plan"

Is there another way to use internet sharing without changing to a custom rom? I tried wifirouter 2.0 via USB but it didn't work (phone said ready, but computer didn't connect to the internet). Phone, or the desktop do not have wifi.

thanks