Android to I2C Control
If you're looking for an off the shelf development board that is going to fit in an area of 1" x 0.5", it's not gonna to happen. Even the smallest MSP board I could find is 1.9" x 1.9", doesn't have USB or I2C functionality, and doesn't even have a power supply:



If that form factor is a hard requirement, then the board will need to be custom. The ADK is open source. So just take the schematic files and do the layout yourself to fit within your desired form factor.