A research topic that is becoming increasingly popular is that of on-board mobile communication, where users on a vehicle are connected to a local network that attaches to the Internet via a mobile router and a wireless link. However, wireless data transmission is less efficient, prone to error and unreliable in a mobile environment. There is a need to make use of multiple access links simultaneously (so-called multihoming), to improve the aggregate bandwidth and the overall service availability on a mobile network. In this paper, we introduce a novel on-board Multihoming Agent for supporting the future on-board multihomed mobile routers. The Multihoming Agent can intelligently stripe user traffics into multiple active WAN interfaces based on the policy in use and the real-time network status and automatically shift user traffics from unavailable links to available ones. We show that by properly deploying the policies defined in the Policy Database and continuously collecting network status, a user can run intelligent load distribution algorithms on top of the mobile router to improve network performance and reliability via our Multihoming Agent.