There’s no easy way of hiding MobileSafari’s useragent.
I’d write their webdepartment an email, blindly rewriting every url to /wap/ just because that particular browser is detected seems like a very silly thing to do.
You can try various web anonymizers although I’m not sure if they hide that bit of information.
Maybe there’s also an app for the iPhone that uses the webkit renderer with a different useragent (1Password and Twitterrific come to my mind) — but those are all stupid workarounds for an even more stupid cause.