You can't actually ever get them to combine for example to increase the speed of a download of a single file from say netflix.
You can to a point use both if you work at it. First you only can have 1 default route so you need to remove one lets say on the wireless. You now must decided what traffic is going to use which connection. Anything you do not want to run on the default connection you need to use the ROUTE ADD command to send it to the proper gateway.
The huge problem is sites are made up of multiple IP blocks and they hide authentication information in cookies that contain your IP. If you were to say put a route in for a server at a site and then the server tells your browser to open another ip and that one goes out...