It seems there is a software for Windows that does that. It creates a local proxy that spreads your network traffic across all available interfaces connected to the Internet.
You can use pretty much anything with enough USB ports. Check out something like http://www.clusterlinks.com/ for easy bridging and managing of connections, like multiple 4g adapters. Be aware, that for any kind of streaming, you generally can't just drop connection from one source and seamlessly pick it up from another. But I guess there is only one way to find out. Be our guinea pig you majestic bastard.
Speedify, iNetFusion, Dispatch-Proxy. > Use multiple Internet connections simultaneously for their combined speed. Everything including uploads, downloads, web browsing, and streaming video can be accelerated by Speedify.