only(easy) way i can think of on how to acomplish this is to use the older version of WMWiRouter
http://global.wmwifirouter.com/consumer/
Make sure to get version prior to 1.5x(1.4x, 1.3x even 0.96 will work) since BT was disabled for TP2s on versions after 1.5("Support from version 1.50. Sharing using Bluetooth not currently supported."). If you however have TP(1) or any other WM smartphone besides TP2 - get the latest version(2.0 atm). Once you get it its very simple and takes couple of clicks to share net over BT as you would over wifi(make BT hotspot). This app will also allow you to share over WiFi and has tons of other great net features(such as USB direct connect for tethering+charging). Shoot me a PM if you have trouble getting this to work or finding the older version, always glad to help fellow ppcgeeker.