Bonding two separate broadband connections into 1 aggregated circuit

[WAprovcom]

I have been tasked to take 2 separate 50Mb broadband internet connections and bond them into a single 100Mb circuit.  This faciility will use Comcast Business Class broadband which I'm assuming will consist of an ISP coax cable connected to a modem with an ethernet handoff.

I am wondering if this is even possible?  I thought of ether-channel but that requires both ends of the ethernet to be configured which is not possible here. How about using a load balancer or WAN accelerator ( I have little knowledge of both of these devices) ? 

[Jjlbgreen]

There might be an easy solution to this if you consider bonding above the IP layer rather than a hardware solution. Sharedband.com provide the software but it might be pushing it to achieve 100mb as currently the fastest Linux routers they have are limited by the processor but it might be worth exploring.