I'm struggling with approx. the same issue. I dont think the term Bridging is right here, its another pure network term defined years back. Instead, I believe you want to have your PC (or Laptop) with 3G Internet (Modem Broadband) access (also known as Wide Wide Area Network or WWAN) to act as a WiFi Access Node (either permanent or temporary). This is treated in several (and its growing) places like here: http://www.itgeekdiary.com/windows-7-as-an-wi-fi-access-point/ or here: Internet connection sharing over WIFI without modifying LAN adapter IP address
In the first link ressource, its described that "..Some wireless broadband providers’ hardware disallows the use of their device in an ICS setup. Microsoft are working on a solution to support all of these and will make an announcement when we have a resolution."
I guess this is what we have to wait for, unless you decide to move to another platform like nix type of OS. Some refers to programs that promise this functionality like this overview site: http://alternativeto.net/software/connectify/ but they can't beat the hardware or driver limitations set by vendors like Huawei. I have a qualified guess that European Union (or Commission) will look into this sort of matter as a protective measure for keeping competitors away, and thus will file a case against these vendors in due time. Hope this gave some comfort even the solution isn't just around the corner... Cheers