When I was running cm7 I used the android power control widget, and I remember there being a option for turning mobile data on/off and other non standard options in the widget. But I cant find it now on grom.
Actually I found one lol, sorry I forgot to post. But I also realized that hydrorom has 5 more options in its power control, one of which is data on/off
I use the Toggle Widgets Pack (from Android Market, now called Google Play) to turn off my 3G - altho it only takes me directly to the settings without having to go through all the motions. It also allows you to turn off Bluetooth and Wireless, etc right from the home screen. I love that widget.