How can I get a non-line of sight communication between computers over distances of 1-5 Kms?

Hi, I am part of a team that participates in rover challenges such as URC (University Rover Challenge), ERC (European Rover Challenge), etc. These competitions, especially URC requires our rovers to travel around 1 Km away from the base station. The major hurdle in this situation is to manage the communication between the base station and the rover. Such competitions only allow specific radio and WiFi frequencies to be used (Pages 4-5 contain rules regarding communications equipment).

I am having trouble finding equipment that can maintain a wireless connection for at least 1 Km. The communication has to be non line-of-sight ready as the rover may have to travel on small hills or in valleys during the competition's tasks. Also, the throughput demands are high compared to low power wireless as the rover would be constantly sending sensor telemetry and multiple video feeds over the wireless link.

Things we have thought of/implemented -

1. Our current solution uses 2.4GHz WiFi with 2x Ubiquiti Nanostation loco M2s at base station and an Ubiquiti Rocket M2 with an Omnidirectional antenna atop our rover. According to our testing this setup is only reliable for up-to 200 meters (line-of-sight (ish), there were minor obstacles in between - couple of small shrubs, elevation change of about 50 cms).
2. Implementing an ad-hoc network by dropping transponders onsite is not possible due to the competition and rover capacity constraints.
3. If choosing equipment with frequencies not used in WiFi (900MHz, 2.4GHz and 5GHz), how can we connect computers to that network for TCP/IP communication?
4. Any solution should have enough penetrating power to pass through small obstacles in line-of-sight such as small hills.
5. According to our testing data-rates on this network should be around 5-6 Mbps to support 4 video feeds at about 800x600 resolution with mjepg compression.
6. Cellular Networks (4G/3G and the likes) cannot be used according to competition rules.

The entire communications system should be completely wireless between the rover and the base station.

I am also open to custom solution designs. Please let me know if anything else is required. Thanks!