IoT devices are quickly becoming a critical source of information about the physical world considered in business processes. Blockchains are a promising platform for such processes if they involve multiple parties with no shared, commonly trusted IT infrastructure. Transacting with a blockchain, however, requires software whose footprint overwhelms many lightweight IoT devices. In this paper we introduce the concept of a blockchain proxy to which an IoT device can offload a large part of this software footprint. The proxy only requires a slim proxy SDK on the device that holds a regular blockchain identity with its own private key, retaining full control of the transactions in the device. We discuss security implications and present cold-chain monitoring as a use case. Preliminary results show significant savings in CPU time and communication bandwidth for the IoT device.